mesa: Remove PROGRAM_WRITE_ONLY register type.

More dead code.  I'm not sure what it was for.

Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

src/mesa/drivers/dri/i965/brw_vs_emit.c

@@ -1010,7 +1010,6 @@ static struct brw_reg get_reg( struct brw_vs_compile *c,
 
    case PROGRAM_LOCAL_PARAM: 
    case PROGRAM_ENV_PARAM: 
-   case PROGRAM_WRITE_ONLY:
    default:
       assert(0);
       return brw_null_reg();

src/mesa/drivers/dri/r200/r200_vertprog.c

@@ -218,7 +218,6 @@ static unsigned long t_src_class(gl_register_file file)
       return VSF_IN_CLASS_PARAM;
    /*
    case PROGRAM_OUTPUT:
-   case PROGRAM_WRITE_ONLY:
    case PROGRAM_ADDRESS:
    */
    default:

src/mesa/program/prog_execute.c

@@ -183,9 +183,6 @@ get_dst_register_pointer(const struct prog_dst_register *dest,
          return dummyReg;
       return machine->Outputs[reg];
 
-   case PROGRAM_WRITE_ONLY:
-      return dummyReg;
-
    default:
       _mesa_problem(NULL,
          "Invalid dest register file %d in get_dst_register_pointer()",

src/mesa/program/prog_print.c

@@ -64,8 +64,6 @@ _mesa_register_file_name(gl_register_file f)
       return "CONST";
    case PROGRAM_UNIFORM:
       return "UNIFORM";
-   case PROGRAM_WRITE_ONLY:
-      return "WRITE_ONLY";
    case PROGRAM_ADDRESS:
       return "ADDR";
    case PROGRAM_SAMPLER: