gdb: Convert language la_print_array_index field to a method

gdb: Convert language la_print_array_index field to a method

This commit changes the language_data::la_print_array_index function
pointer member variable into a member function of language_defn.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_print_array_index): Delete function, move
	implementation to...
	(ada_language::print_array_index): ...here.
	(ada_language_data): Delete la_print_array_index initializer.
	* c-lang.c (c_language_data): Likewise.
	(cplus_language_data): Likewise.
	(minimal_language_data): Likewise.
	* d-lang.c (d_language_data): Likewise.
	* f-lang.c (f_language_data): Likewise.
	* go-lang.c (go_language_data): Likewise.
	* language.c (default_print_array_index): Delete function, move
	implementation to...
	(language_defn::print_array_index): ...here.
	(unknown_language_data): Delete la_print_array_index initializer.
	(auto_language_data): Likewise.
	* language.h (struct language_data): Delete la_print_array_index
	field.
	(language_defn::print_array_index): New member function.
	(LA_PRINT_ARRAY_INDEX): Update.
	(default_print_array_index): Delete declaration.
	* m2-lang.c (m2_language_data): Delete la_print_array_index
	initializer.
	* objc-lang.c (objc_language_data): Likewise.
	* opencl-lang.c (opencl_language_data): Likewise.
	* p-lang.c (pascal_language_data): Likewise.
	* rust-lang.c (rust_language_data): Likewise.