nir,amd: remove trinary_minmax opcodes

These consist of the variations nir_op_{i|u|f}{min|max|med}3 which are either
lowered in the backend (LLVM) anyway or can be recombined by the backend (ACO).

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6421>

src/amd/compiler/aco_instruction_selection_setup.cpp

@@ -600,9 +600,6 @@ void init_context(isel_context *ctx, nir_shader *shader)
                   case nir_op_fsub:
                   case nir_op_fmax:
                   case nir_op_fmin:
-                  case nir_op_fmax3:
-                  case nir_op_fmin3:
-                  case nir_op_fmed3:
                   case nir_op_fneg:
                   case nir_op_fabs:
                   case nir_op_fsat: