Unify all operators into std-operator.def

This removes ada-operator.def and fortran-operator.def, merging their
contents into std-operator.def.

Note that the comment for OP_EXTENDED0 is a bit wrong.  IMO this
constant could be removed, as it is only used for a single assert that
does not provide much value.  However, I haven't done so here.

gdb/ChangeLog
2020-12-09  Tom Tromey  <tromey@adacore.com>

	* expprint.c (op_name): Update.
	* expression.h (enum exp_opcode): Update.
	* std-operator.def: Add more opcodes.
	* ada-operator.def, fortran-operator.def: Remove, moving contents
	into std-operator.def.

gdb/expprint.c

@@ -704,8 +704,6 @@ op_name (enum exp_opcode opcode)
     case name:		\
       return #name ;
 #include "std-operator.def"
-#include "ada-operator.def"
-#include "fortran-operator.def"
 #undef OP
     }
 }