Remove confusing FIXME.

- After 2.6 is released we still have to support older ruby
  versions so we cannot remove this.
- We can only remove it once we stop supporting RUBY_VERSION < 2.6.
- We search for RUBY_VERSION uses when dropping old versions and
  do not need a FIXME.

[ci skip]

Author: myronmarston

lib/rspec/core/configuration_options.rb

@@ -168,8 +168,6 @@ def args_from_options_file(path)
       end
 
       def options_file_as_erb_string(path)
-        # FIXME: Consider removing the following conditional branch after Ruby 2.6 is released.
-        #        https://github.com/ruby/ruby/commit/cc777d09f44fa909a336ba14f3aa802ffe16e010
         if RUBY_VERSION >= '2.6'
           ERB.new(File.read(path), :trim_mode => '-').result(binding)
         else