Remove two Ada opcodes

Remove two Ada opcodes

The OP_ATR_MIN and OP_ATR_MAX constants aren't truly needed.
Internally, they are converted to BINOP_MIN and BINOP_MAX.  This patch
removes them in favor of simple reuse.

gdb/ChangeLog
2021-03-08  Tom Tromey  <tom@tromey.com>

	* std-operator.def (OP_ATR_MIN, OP_ATR_MAX): Remove.
	* ada-lang.c (ada_binop_minmax): Update.
	* ada-exp.h (ada_binop_min_operation, ada_binop_max_operation):
	Use BINOP_MIN and BINOP_MAX.