autoscripts/prerm-{py3,pypy}clean: Use sed instead of perl

Using perl in maintscripts is problematic because Perl may no longer be installed in the future by the time the user purges the Python packages that use dh-python.

The specific use of perl in these prerm maintscripts can be easily replaced with an equivalent sed invocation.

autoscripts/prerm-py3clean

 if command -v py3clean >/dev/null 2>&1; then
 	py3clean -p #PACKAGE# #ARGS#
 else
-	dpkg -L #PACKAGE# | perl -ne 's,/([^/]*)\.py$,/__pycache__/\1.*, or next; unlink $_ or die $! foreach glob($_)'
+	dpkg -L #PACKAGE# | sed -En -e '/^(.*)\/(.+)\.py$/s,,rm "\1/__pycache__/\2".*,e'
 	find /usr/lib/python3/dist-packages/ -type d -name __pycache__ -empty -print0 | xargs --null --no-run-if-empty rmdir
 fi