Drop x86-mswin32-60 support
Drop x86-mswin32-60 support

The above platform was only necessary during the transition time of
One-Click Ruby Installer (OCI) to RubyInstaller back when 1.8.6
was released.

That was 7 years ago and had to die at some point, why not now?

tjschuck/rake-compiler-dev-box,copiousfreetime/rake-compiler-dev-box,tjschuck/rake-compiler-dev-box,ruby-concurrency/rake-compiler-dev-box,ruby-concurrency/rake-compiler-dev-box,flavorjones/rake-compiler-dev-box,copiousfreetime/rake-compiler-dev-box,flavorjones/rake-compiler-dev-box,flavorjones/rake-compiler-dev-box,copiousfreetime/rake-compiler-dev-box,ruby-concurrency/rake-compiler-dev-box,tjschuck/rake-compiler-dev-box,flavorjones/rake-compiler-dev-box,ruby-concurrency/rake-compiler-dev-box,tjschuck/rake-compiler-dev-box,copiousfreetime/rake-compiler-dev-box