Remove Xcode prerelease warnings.

At this point we probably do want to know about issues that crop up in
betas so we can fix them before the new version of Xcode is released.
Additionally, this doesn't really work well any more with our new
tag-based workflow as it means we need to cut a new tag immediately
after a new Xcode is released.

Library/Homebrew/extend/os/mac/diagnostic.rb

@@ -4,7 +4,6 @@ module Homebrew
       def development_tools_checks
         %w[
           check_for_unsupported_macos
-          check_for_prerelease_xcode
           check_for_bad_install_name_tool
           check_for_installed_developer_tools
           check_xcode_license_approved
@@ -50,21 +49,6 @@ module Homebrew
         EOS
       end
 
-      def check_for_prerelease_xcode
-        return if ARGV.homebrew_developer?
-        # Running a pre-release Xcode on a pre-release OS is expected
-        # and likely to cause less problems than a stable Xcode will.
-        return if OS::Mac.prerelease?
-        return unless MacOS::Xcode.installed?
-        return unless MacOS::Xcode.prerelease?
-
-        <<-EOS.undent
-          You are using a pre-release version of Xcode.
-          You may encounter build failures or other breakages.
-          Please create pull-requests instead of filing issues.
-        EOS
-      end
-
       def check_xcode_up_to_date
         return unless MacOS::Xcode.installed?
         return unless MacOS::Xcode.outdated?

Library/Homebrew/os/mac/xcode.rb

@@ -36,11 +36,6 @@ module OS
         version < minimum_version
       end
 
-      def prerelease?
-        # TODO: bump to version >= "8.4" after Xcode 8.3 is stable.
-        Version.new(version) >= "8.3"
-      end
-
       def outdated?
         Version.new(version) < latest_version
       end