[JOIN] Fix removal of protected files

[JOIN] Fix removal of protected files

In the join case, since we are not extracting files, we don't really want
to remove the files. So, in this case, remove all files that the
delete_regex matches, but not the files that are protected.

This fixes the following case:
==========================================
X.rar.par2
X.rar.vol0+1.par2
...
X.rar.001
X.rar.002
...

Where X.rar is the only protected file. When the process completes, X.rar
will be the only file left.

Signed-off-by: Ira W. Snyder <devel@irasnyder.com>