ir_to_mesa: Rename ir_to_mesa_emit_*_opX methods to emit_*.
ir_to_mesa: Rename ir_to_mesa_emit_*_opX methods to emit_*.

There's really no need for a prefix on member functions, and overloading
takes care of the _op1/_op2 distinction quite nicely.  Eric already made
a similar change in the i965 FS backend.

Reviewed-by: Ian Romanick <2b237cafb16dc45038e85df6c85e74e6d899eba9@intel.com>

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