debian/rules: Drop override_dh_strip again

... now deleting it from the .PHONY target too. Its left-over presence in
.PHONY caused dh_strip to be skipped entirely, leaving binaries unstripped.

See https://salsa.debian.org/aqbanking-team/pkg-libgwenhywfar/-/merge_requests/1
for further details.

Git-Dch: full