Fix MuxLookup old API deprecation (#3113) (#3114)

It seems that deprecations on methods that are macro expanded away do
not actually trigger a deprecation warning. Instead, we will just accept
no source locator on the deprecated API (no released version of Chisel
has the source locator).

(cherry picked from commit 847343a3

)

Co-authored-by: Jack Koenig <koenig@sifive.com>
Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>