Remove Fast Refresh bail-out in DeltaCalculator on certain errors

Summary:
Since D51665495, a transform or resolution error encountered while processing modified files will throw *before any change is committed to `Graph`'s state*, so if `DeltaCalculator` catches an error we can be confident `Graph` is still in a good state.

Previously this might've left a modification partially applied to the graph (I assume that's what's meant by "weird state" in the comment here), so `DeltaCalculator` would attempt to detect that and force a reset update. That creates extra work both for Metro (especially as the next modification might not fix the error, we would re-traverse the whole graph on any change perhaps multiple times), and the client, having a full reset to process. It's no longer necessary.

(Note that in any case this safety net had gaps - it was always possible for a bad update to both add and remove modules such that the overall size didn't change.)

Changelog:
```
**[Fix]:** Don't unnecessarily reset Fast Refresh after recovering from certain transform or resolution errors.
```

Reviewed By: GijsWeterings

Differential Revision: D52193122

fbshipit-source-id: 65516257edb0a2cad79c3346f946ab960b7dfc70

packages/metro/src/DeltaBundler/DeltaCalculator.js

@@ -133,8 +133,6 @@ class DeltaCalculator<T> extends EventEmitter {
 
     let result;
 
-    const numDependencies = this._graph.dependencies.size;
-
     try {
       result = await this._currentBuildPromise;
     } catch (error) {
@@ -146,13 +144,6 @@ class DeltaCalculator<T> extends EventEmitter {
       deletedFiles.forEach((file: string) => this._deletedFiles.add(file));
       addedFiles.forEach((file: string) => this._addedFiles.add(file));
 
-      // If after an error the number of modules has changed, we could be in
-      // a weird state. As a safe net we clean the dependency modules to force
-      // a clean traversal of the graph next time.
-      if (this._graph.dependencies.size !== numDependencies) {
-        this._graph.dependencies.clear();
-      }
-
       throw error;
     } finally {
       this._currentBuildPromise = null;