patchwork-apply.sh: remove explicit commit references

patchwork-apply.sh: remove explicit commit references

Mentioning explicit commit hashes proved to be unreliable, especially
when frequently rebasing the tree, so only post generic repository
references instead.

Also avoid clobbering subjects in the form "[TAG] subject [foo]" where
the prevously used sed pattern would reduce the entire subject to an
empty string.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>