lang/ruby27: throw out irb, ri, rdoc from lang/ruby27

because they're provided as "default gem" since Ruby 2.6.

We provide "default gem"s as gem ports rather than a part of lang/ruby*
port. files/patch-tool_rbinstall.rb makes not to install such default gems
however hollow wrapper scripts bin/{irb,ri,rdoc} and their manpages were
still left.

This commit intend to move out such wrapper scripts and manpages to gem
ports completely.

PR: 243888
Submitted by: Yasuhiro KIMURA <yasu@utahime.org> (initial revision)

		meta (myself)

Differential Revision: https://reviews.freebsd.org/D23514