Mk/bsd.ruby.mk: Remove RUBY_{PATCHLEVEL,RELVERSION,RELVERSION_CODE,RUBY_DISTVERSION}

1. RUBY_PATCHLEVEL has been 0 since Ruby 2.1
2. After RUBY_PATCHLEVEL is removed , RUBY_RELVERSION and RUBY_VERSION are always same value and it also applies to RUBY_RELEVERSION_CODE and RUBY_VERSION_CODE
3. RUBY_PATCHLEVEL is only used to set value of CPE_UPDATE in lang/ruby2[456] and setting CPE_UPDATE is optional
4. RUBY_RELEVERSION is only used to set value of CPE_VERSION in lang/ruby2[456] but as is describled in 2, it can be replased with RUBY_VERSION
5. RUBY_RELVERSION_CODE is not used anywhere

PR: 241473
Submitted by: Yasuhiro KIMURA <yasu@utahime.org>
Reviewed by: sunpoet