gallium: remove multiple aliases for TGSI opcodes

gallium: remove multiple aliases for TGSI opcodes

This is a source of ongoing confusion.  TGSI has multiple names for
opcodes where the same semantics originate in multiple shader APIs.

For instance, TGSI includes both Mesa/GLSL and DX/SM30 names for
opcodes with the same semantics, but aliases those names to the same
underlying opcode number.

This makes it very difficult to visually inspect two sets of opcodes
(eg in state tracker & driver) and check if they implement the same
functionality.

This patch arbitarily rips out the versions of the opcodes not currently
favoured by the mesa state tracker and leaves us with a single name
for each distinct operation.