Eliminate UNOP_MEMVAL_TLS

Eliminate UNOP_MEMVAL_TLS

Since minsym references now go via OP_VAR_MSYM_VALUE, UNOP_MEMVAL_TLS
is no longer used anywhere.

gdb/ChangeLog:
2017-09-04  Pedro Alves  <palves@redhat.com>

	* eval.c (evaluate_subexp_standard): Remove UNOP_MEMVAL_TLS
	handling.
	* expprint.c (print_subexp_standard, dump_subexp_body_standard):
	Ditto.
	* parse.c (operator_length_standard, operator_check_standard):
	Ditto.
	* std-operator.def (UNOP_MEMVAL_TLS): Delete.