Remove ALL_EXTENSION_LANGUAGES and ALL_ENABLED_EXTENSION_LANGUAGES

Remove ALL_EXTENSION_LANGUAGES and ALL_ENABLED_EXTENSION_LANGUAGES

This removes the ALL_EXTENSION_LANGUAGES and
ALL_ENABLED_EXTENSION_LANGUAGES macros, in favor of ordinary
iterators.  For ALL_ENABLED_EXTENSION_LANGUAGES, I chose to simply
inline the check, as that seemed simpler than trying to make
filtered_iterator work for std::array.  (As an aside, this sort of
thing will be easier once we can use the ranges library...)

gdb/ChangeLog
2020-05-08  Tom Tromey  <tom@tromey.com>

	* extension.c (extension_languages): Now a std::array.
	(ALL_EXTENSION_LANGUAGES): Remove.
	(get_ext_lang_defn, get_ext_lang_of_file)
	(eval_ext_lang_from_control_command): Update.
	(finish_ext_lang_initialization)
	(auto_load_ext_lang_scripts_for_objfile)
	(ext_lang_type_printers::ext_lang_type_printers)
	(apply_ext_lang_type_printers)
	(ext_lang_type_printers::~ext_lang_type_printers)
	(apply_ext_lang_val_pretty_printer, apply_ext_lang_frame_filter)
	(preserve_ext_lang_values, get_breakpoint_cond_ext_lang)
	(breakpoint_ext_lang_cond_says_stop, check_quit_flag)
	(get_matching_xmethod_workers, ext_lang_colorize)
	(ext_lang_before_prompt): Update.
	(ALL_ENABLED_EXTENSION_LANGUAGES): Remove.