Remove remaining traces of Webmock (#511)

Author: andyw8

gemfiles/Gemfile-rails-main

@@ -19,7 +19,6 @@ gem "sorbet-static-and-runtime", platforms: :ruby
 gem "tapioca", "~> 0.11", require: false, platforms: :ruby
 gem "psych", "~> 5.1", require: false
 gem "rails", github: "rails/rails", branch: "main"
-gem "webmock"
 
 platforms :mingw, :x64_mingw, :mswin, :jruby do
   gem "tzinfo"