brw: Drop INTERPOLATE_AT mlen handling from size_read()

FS_OPCODE_INTERPOLATE_AT_{SAMPLE,SHARED_OFFSET} never have a mlen set.
They are lowered to SHADER_OPCODE_SEND in logical send lowering, at
which point they acquire an mlen, but cease to be those opcodes.

Reviewed-by: Caio Oliveira <caio.oliveira@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33297>

src/intel/compiler/brw_inst.cpp

@@ -535,12 +535,6 @@ brw_inst::size_read(const struct intel_device_info *devinfo, int arg) const
       }
       break;
 
-   case FS_OPCODE_INTERPOLATE_AT_SAMPLE:
-   case FS_OPCODE_INTERPOLATE_AT_SHARED_OFFSET:
-      if (arg == 0)
-         return mlen * REG_SIZE;
-      break;
-
    case BRW_OPCODE_PLN:
       if (arg == 0)
          return 16;