rubocop: In-line disables for Style/{Class,Global}Vars

- Other occurrences of `@@` and `$` variables are individually disabled
  in-line in other files.
- So let's follow the same pattern for Homebrew/homebrew-cask developer
  scripts, since there are only a few.

Library/.rubocop.yml

@@ -342,11 +342,6 @@ Style/BlockDelimiters:
   Exclude:
     - "Homebrew/**/*_spec.rb"
 
-# TODO: remove this when possible.
-Style/ClassVars:
-  Exclude:
-    - "**/developer/bin/*"
-
 # Use consistent style for better readability.
 Style/CollectionMethods:
   Enabled: true
@@ -386,11 +381,6 @@ Style/FrozenStringLiteralComment:
     - "**/*.rbi"
     - "**/Brewfile"
 
-# TODO: remove this when possible.
-Style/GlobalVars:
-  Exclude:
-    - "**/developer/bin/*"
-
 # potential for errors in formulae too high with this
 Style/GuardClause:
   Exclude: