gdb: remove LA_EMIT_CHAR macro

Now that every use of the LA_EMIT_CHAR macro is within a language_defn
member function we can simply call the emitchar member function
directly instead of using the LA_EMIT_CHAR macro.

If we are ever inside a language object, for example, cplus_language,
while current_language points at something other than cplus_language
then this commit will result in a change in behaviour.  However, I
believe if we did have such a difference then this would be a bug in
GDB.  AS such I'm going to claim there _should_ be no user visible
changes from this commit.

gdb/ChangeLog:

	* c-lang.c (language_defn::printchar): Call emitchar, not
	LA_EMIT_CHAR.
	* f-lang.h (f_language::printchar): Likewise.
	* language.h (LA_EMIT_CHAR): Delete macro.
	* rust-lang.c (rust_language::printchar): Call emitchar, not
	LA_EMIT_CHAR.