`gtk4-macros`: Blueprint sources should not include the `using Gtk 4.0` declaration by default

[jgcodes2020]

Bug description
The current implementation of Blueprint templates automatically prepends the declaration using Gtk 4.0;. This is part of Blueprint's syntax, and omitting it in a Blueprint file causes the language server to error out.

Fixing it is a simple one-line change in gtk4-macros/blueprint.rs, specifically deleting line 17 here:

gtk4-rs/gtk4-macros/src/blueprint.rs

Lines 16 to 20 in 3a99628

	let mut stdin = compiler.stdin.take().unwrap();
	stdin.write_all(b"using Gtk 4.0;\n")?;
	stdin.write_all(blueprint)?;
	drop(stdin);

Obviously the tests need to be modified, but that's not a big problem.

Backtrace
N/A

[jgcodes2020]

Seems like this was fixed, I'll close this issue for now.