parse.y: remove "f" suffix [ruby-core:57966] [Feature #9042]

revert r42847 "test_string.rb: add test string encoding"

revert r42846 "parse.y: freeze in advance to reduce objects"

revert r42843 "parse.y: deduplicate frozen string literals"

revert r42780 "test_string.rb: yet another test"

revert r42779 "parse.y: valid suffix word only"

revert r42778 "test_string.rb: remove duplicated code"

revert r42775 "parse.y: force_encoding"

This reverts commit 93ea04ecec7639ca8d0e58948e78461434782ecc.

revert r42773 "Add frozen string literals"

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43634 b2dd03c8-39d4-4d8f-98ff-823fe69b080e