if there are multiple user-level template dirs then we should be able to
remove/rename content in all of them, not just the default writable target.

The target scenario here is to default to ~/Templates when it exists as the
template dir, but to retain ~/.config/libreoffice/user/template in the dir for
any pre-existing templates and to treat both as equivalent in terms of removing
their content etc.

i#66157# wanted to avoid remove extensions templates and other internal
ones, so rework that logic to instead just be hands off internal templates
and allow modification of the remainder

Change-Id: I56afe991d4297ba692e914ae95ea02d68553f60a