gdb: Remove language_data struct

gdb: Remove language_data struct

The language_data type, from which language_defn inherits, is now
empty, and this commit removes it.

Each language is updated to no longer create and use a language_data
struct.

There should be no user visible changes after this commit.

gdb/ChangeLog:

	* ada-lang.c (ada_language_data): Delete.
	(ada_language): Remove references to ada_language_data.
	* c-lang.c (c_language_data): Delete.
	(c_language): Remove references to c_language_data.
	(cplus_language_data): Delete.
	(cplus_language): Remove references to cplus_language_data.
	(asm_language_data): Delete.
	(asm_language): Remove references to asm_language_data.
	(minimal_language_data): Delete.
	(minimal_language): Remove references to minimal_language_data.
	* d-lang.c (d_language_data): Delete.
	(d_language): Remove references to d_language_data.
	* f-lang.c (f_language_data): Delete.
	(f_language): Remove references to f_language_data.
	* go-lang.c (go_language_data): Delete.
	(go_language): Remove references to go_language_data.
	* language.c (unknown_language_data): Delete.
	(unknown_language): Remove references to unknown_language_data.
	(auto_language_data): Delete.
	(auto_language): Remove references to auto_language_data.
	* language.h (language_data): Delete struct.
	(language_defn): No longer inherit from language_data.
	* m2-lang.c (m2_language_data): Delete.
	(m2_language): Remove references to m2_language_data.
	* objc-lang.c (objc_language_data): Delete.
	(objc_language): Remove references to objc_language_data.
	* opencl-lang.c (opencl_language_data): Delete.
	(opencl_language): Remove references to opencl_language_data.
	* p-lang.c (pascal_language_data): Delete.
	(pascal_language): Remove references to pascal_language_data.
	* rust-lang.c (rust_language_data): Delete.
	(rust_language): Remove references to rust_language_data.