rust: Fix bloat issue in recent rust updates

rust: Fix bloat issue in recent rust updates

Remove the "src/gcc" directory from the Rust source code to reduce the
filesystem build space.

In Rust 1.83 (and 1.84), a full GCC-14 tree was included, which caused
the tar.xz archive to increase by 128 MB and the unpacked sources to
grow by 1.3 GB. This was an upstream error that has been resolved in
Rust 1.85.

After updating to Rust 1.85 we can revert this removal of "src/gcc"

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>