Remove usages of HOMEBREW_INSTALL_BUNDLER_GEMS_FIRST

Library/Homebrew/brew.rb

@@ -17,12 +17,6 @@ if RUBY_X < 2 || (RUBY_X == 2 && RUBY_Y < 6)
   raise "Homebrew must be run under Ruby 2.6! You're running #{RUBY_VERSION}."
 end
 
-# Load Bundler first of all if it's needed to avoid Gem version conflicts.
-if ENV["HOMEBREW_INSTALL_BUNDLER_GEMS_FIRST"]
-  require_relative "utils/gems"
-  Homebrew.install_bundler_gems!
-end
-
 # Also define here so we can rescue regardless of location.
 class MissingEnvironmentVariables < RuntimeError; end
 

Library/Homebrew/brew.sh

@@ -378,11 +378,6 @@ then
   esac
 fi
 
-if [[ "$HOMEBREW_COMMAND" = "audit" || "$HOMEBREW_COMMAND" = "style" ]]
-then
-  export HOMEBREW_INSTALL_BUNDLER_GEMS_FIRST="1"
-fi
-
 # Set HOMEBREW_DEV_CMD_RUN for users who have run a development command.
 # This makes them behave like HOMEBREW_DEVELOPERs for brew update.
 if [[ -z "$HOMEBREW_DEVELOPER" ]]