Mk/bsd.port.mk: Drop the strip parameter from PATCHFILES passed to do-fetch.sh

[0mp]

Summary

After recent changes to handling of do-fetch.sh in bsd.port.mk, the
strip parameters (e.g., ":-p1") are no longer dropped before do-fetch.sh
receives patch files.

As a result, a strip parameter of a patch file might be interpreted as a
group instead and get prepended to the patch file, resulting in warnings
like:

$ make makesum
===>  License MIT accepted by the user
=> e3efbb5923f638b38087a3f616906d9d4fdaf6f2.patch doesn't seem to exist in /var/cache/distfiles.
=> Attempting to fetch p1e3efbb5923f638b38087a3f616906d9d4fdaf6f2.patch
fetch: p1e3efbb5923f638b38087a3f616906d9d4fdaf6f2.patch: No such file or directory

Fixes: 076687302bff Mk: fix checksum/fetch/makesum with large distfiles set
Sponsored by: fme AG

[0mp]

s/:p/:-p/

[mat]

Thank you.