rust: don't select CONSTRUCTORS

This was originally part of commit 4b9a68f2e59a0 ("rust: add support for
static synchronisation primitives") from the old Rust branch, which used
module constructors to initialize globals containing various
synchronisation primitives with pin-init. That commit has never been
upstreamed, but the `select CONSTRUCTORS` statement ended up being
included in the patch that initially added Rust support to the Linux
Kernel.

We are not using module constructors, so let's remove the select.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Cc: stable@vger.kernel.org
Fixes: 2f7ab126 ("Kbuild: add Rust support")
Link: https://lore.kernel.org/r/20240308-constructors-v1-1-4c811342391c@google.com


Signed-off-by: Miguel Ojeda <ojeda@kernel.org>