anv/compiler: Delete legacy clipping code
anv/compiler: Delete legacy clipping code

This is a Vulkan driver.  We don't need legacy clipping stuff and, even if
we did, we don't plan on supporting pre-Sandybridge anyway.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler