Revert "nir/copy_propagate: do not copy-propagate MOV srcs with source modifiers"
Revert "nir/copy_propagate: do not copy-propagate MOV srcs with source modifiers"

The change proposed in the review leads to piglit regressions because
is_move() is used in other places and relies on the checks for source
modifiers to be there.

Revert this until we agree on a better solution.

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler