Drop patch to lower minimum ruby version (already satsfied in buster)

debian/patches/0640-relax-ruby-version.patch

@@ -1,13 +0,0 @@
-Debian's ruby has the latest security patches applied
-
---- a/lib/system_check/app/ruby_version_check.rb
-+++ b/lib/system_check/app/ruby_version_check.rb
-@@ -7,7 +7,7 @@ module SystemCheck
-       set_check_pass -> { "yes (#{self.current_version})" }
- 
-       def self.required_version
--        @required_version ||= Gitlab::VersionInfo.new(2, 5, 3)
-+        @required_version ||= Gitlab::VersionInfo.new(2, 3, 3)
-       end
- 
-       def self.current_version

debian/patches/series

@@ -19,7 +19,6 @@
 0610-source-init-functions.patch
 0620-pid-log-paths.patch
 0630-fix-mail-room-path.patch
-0640-relax-ruby-version.patch
 0660-fix-gitlab-yml-path.patch
 0690-debian-usage-ping.patch
 0700-add-salsa-link-to-help.patch