Revert "Update specs for Refinements conforming to the latest spec described at <https://bugs.ruby-lang.org/projects/ruby-trunk/wiki/RefinementsSpec>."

This reverts commit 45fe77547a063284cbc04faf6708a426ed68f712.
Revert "MRI r37619 remove Kernel#using, and add main.using instead"

This reverts commit 51ecb834238a162081c57c03bbca4718d37a5963.
Revert "Add missing string_refinement.rb file."

This reverts commit ad6a980d7ad4b5c2d10df64933180089f493e3c9.
Revert "Add additional examples from a_matsuda's talk."

This reverts commit d9bd1363d29d73ee32c06ee73dd0afb2f3ddaf05.
Revert "using is defined on Kernel, not Module."

This reverts commit ee0539fbf8381e9dfc1ec2290d91f7d7d161d665.
Revert "Initial refinement specs; not pretty, but it's a start."

This reverts commit f603267b0afb2d9760d5a480078ee8cbb8a0984d.