[circt] Stop dropping RunFirrtlTransformAnnotation (#3001)

Remove dropping of RunFirrtlTransformAnnotation.  This isn't necessary
to drop as firtool will drop these if it sees them.  There is utility in
_not_ dropping these as it removes a dependency from the "circt" package
on transforms that will be removed from the "firrtl" package on the
chisel5 branch.

Signed-off-by: Schuyler Eldridge <schuyler.eldridge@sifive.com>