rubocop: Move Style/DocumentationMethod into the other file

Library/.rubocop.yml

@@ -367,10 +367,6 @@ Style/Documentation:
     - "**/{Formula,Casks}/**/*.rb"
     - "**/*.rbi"
 
-Style/DocumentationMethod:
-  Include:
-    - "Homebrew/formula.rb"
-
 # This is quite a large change, so don't enforce this yet for formulae.
 # We should consider doing so in the future, but be aware of the impact on third-party taps.
 Style/FetchEnvVar:

Library/Homebrew/.rubocop.yml

@@ -60,6 +60,10 @@ Style/Documentation:
     - utils/string_inreplace_extension.rb
     - version.rb
 
+Style/DocumentationMethod:
+  Include:
+    - "formula.rb"
+
 Style/HashAsLastArrayItem:
   Exclude:
     - "test/utils/spdx_spec.rb"