Don't bundle node-pre-gyp (#5520)

Bundling node-pre-gyp was only needed for node v4 and earlier.

Remove it to avoid errors like:

> npm ERR! enoent ENOENT: no such file or directory, rename '/home/circleci/project/node_modules/node_or_tools/node_modules/abbrev' -> '/home/circleci/project/node_modules/node_or_tools/node_modules/.abbrev.DELETE'

More context: mapbox/node-pre-gyp#260 (comment)

package.json

@@ -62,7 +62,6 @@
     "mkdirp",
     "nan",
     "node-cmake",
-    "node-pre-gyp",
     "rimraf"
   ],
   "main": "lib/index.js",