make more use of YAML anchors in dependencies.yaml (#16597)

Contributes to rapidsai/build-planning#33

Follow-up to #16299

This proposes some simplifications to `dependencies.yaml`. It's not intended to change any behavior.

* more use of YAML anchors for requirements that are intended to be identical to each other
* eliminating the `pylibcudf_build_dep` dependency group that was introduced in #16299, in favor of just tracking the `pylibcudf` build dependency alongside `cudf`'s `rmm` build dependency in the existing `build_python_cudf` group
  - *(sorry I'd missed that in the review on #16299)*

I found myself starting to make similar changes in the PR breaking up these packages into more (splitting out a `libcudf` in #15483) and thought they'd be better as a standalone PR.

Authors:
  - James Lamb (https://github.com/jameslamb)

Approvers:
  - Bradley Dice (https://github.com/bdice)

URL: #16597

dependencies.yaml

@@ -96,7 +96,6 @@ files:
       - build_base
       - build_python_common
       - build_python_cudf
-      - pylibcudf_build_dep
   py_run_cudf:
     output: pyproject
     pyproject_dir: python/cudf
@@ -383,12 +382,12 @@ dependencies:
               cuda: "12.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu12==24.10.*,>=0.0.0a0
+              - &rmm_cu12 rmm-cu12==24.10.*,>=0.0.0a0
           - matrix:
               cuda: "11.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu11==24.10.*,>=0.0.0a0
+              - &rmm_cu11 rmm-cu11==24.10.*,>=0.0.0a0
           - {matrix: null, packages: [*rmm_unsuffixed]}
   build_python_cudf:
     common:
@@ -412,34 +411,18 @@ dependencies:
               cuda: "12.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu12==24.10.*,>=0.0.0a0
-              - pylibcudf-cu12==24.10.*,>=0.0.0a0
+              - &pylibcudf_cu12 pylibcudf-cu12==24.10.*,>=0.0.0a0
+              - *rmm_cu12
           - matrix:
               cuda: "11.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu11==24.10.*,>=0.0.0a0
-              - pylibcudf-cu11==24.10.*,>=0.0.0a0
-          - {matrix: null, packages: [*rmm_unsuffixed]}
-  pylibcudf_build_dep:
-    common:
-      - output_types: conda
-        packages:
-          - &pylibcudf_unsuffixed pylibcudf==24.10.*,>=0.0.0a0
-    specific:
-      - output_types: [pyproject]
-        matrices:
-          - matrix:
-              cuda: "12.*"
-              cuda_suffixed: "true"
-            packages:
-              - pylibcudf-cu12==24.10.*,>=0.0.0a0
+              - &pylibcudf_cu11 pylibcudf-cu11==24.10.*,>=0.0.0a0
+              - *rmm_cu11
           - matrix:
-              cuda: "11.*"
-              cuda_suffixed: "true"
             packages:
-              - pylibcudf-cu11==24.10.*,>=0.0.0a0
-          - {matrix: null, packages: [*pylibcudf_unsuffixed]}
+              - &pylibcudf_unsuffixed pylibcudf==24.10.*,>=0.0.0a0
+              - *rmm_unsuffixed
   libarrow_build:
     common:
       - output_types: conda
@@ -677,12 +660,12 @@ dependencies:
               cuda: "12.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu12==24.10.*,>=0.0.0a0
+              - *rmm_cu12
           - matrix:
               cuda: "11.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu11==24.10.*,>=0.0.0a0
+              - *rmm_cu11
           - {matrix: null, packages: [*rmm_unsuffixed]}
   run_cudf:
     common:
@@ -728,7 +711,7 @@ dependencies:
               cuda: "12.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu12==24.10.*,>=0.0.0a0
+              - *rmm_cu12
               - pynvjitlink-cu12>=0.0.0a0
           - matrix:
               cuda: "12.*"
@@ -740,7 +723,7 @@ dependencies:
               cuda: "11.*"
               cuda_suffixed: "true"
             packages:
-              - rmm-cu11==24.10.*,>=0.0.0a0
+              - *rmm_cu11
               - cubinlinker-cu11
               - ptxcompiler-cu11
           - matrix:
@@ -874,12 +857,12 @@ dependencies:
               cuda: "12.*"
               cuda_suffixed: "true"
             packages:
-              - pylibcudf-cu12==24.10.*,>=0.0.0a0
+              - *pylibcudf_cu12
           - matrix:
               cuda: "11.*"
               cuda_suffixed: "true"
             packages:
-              - pylibcudf-cu11==24.10.*,>=0.0.0a0
+              - *pylibcudf_cu11
           - {matrix: null, packages: [*pylibcudf_unsuffixed]}
   depends_on_cudf:
     common: