gdb: remove some uses of LA_PRINT_STRING

gdb: remove some uses of LA_PRINT_STRING

This commit removes some, but not all, uses of LA_PRINT_STRING.  In
this commit I've removed those uses where there is an obvious language
object on which I can instead call the printstr method.

In the remaining 3 uses it is harder to know if the correct thing is
to call printstr on the current language, or on a specific language.
Currently obviously, we always call on the current language (as that's
what LA_PRINT_STRING does), and clearly this behaviour is good enough
right now, but is it "right"?  I've left them for now and will give
them more thought in the future.

gdb/ChangeLog:

	* expprint.c (print_subexp_standard): Replace uses of
	LA_PRINT_STRING.
	* f-valprint.c (f_language::value_print_inner): Likewise.
	* guile/scm-pretty-print.c (ppscm_print_string_repr): Likewise.
	* p-valprint.c (pascal_language::value_print_inner): Likewise.
	* python/py-prettyprint.c (print_string_repr): Likewise.