program: Remove incorrect comment about OPCODE_TXD.

The table in prog_instruction.h is correct.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Brian Paul <brianp@vmware.com>

src/mesa/program/prog_execute.c

@@ -1203,7 +1203,7 @@ _mesa_execute_program(struct gl_context * ctx,
             store_vector4(inst, machine, color);
          }
          break;
-      case OPCODE_TXD:         /* GL_NV_fragment_program only */
+      case OPCODE_TXD:
          /* Texture lookup w/ partial derivatives for LOD */
          {
             GLfloat texcoord[4], dtdx[4], dtdy[4], color[4];