tools: add checkstyle --no-clippy

checkstyle and checkbuild run the same clippy command and differ only in
which triples they cover, so running both at commit time checks the
native architecture twice. Skip it in checkstyle and leave it to
checkbuild, which also covers the cross-compiled architecture.

The two then share no work, so running them concurrently takes a
Rust-touching verification from 37s to 19s. checkstyle keeps clippy by
default because CI runs no other clippy.

Signed-off-by: Riccardo Mancini <mancio@amazon.com>