bindings: rust: Allow reusing locally installed gpio library

bindings: rust: Allow reusing locally installed gpio library

The rust crates builds fine when built with the 'make' command, as
static linking works fine. But when referenced from a remote rust crate,
it gives following error:

error: could not find native static library `gpiod`, perhaps an -L flag is missing?

This happens since we only support 'static' LIB-KIND currently. Remove
the same to allow others to work too.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>