fixup! use new config API for worktree configurations of submodules

DONE: Add removal function (at least for paths)
do not die on error of parsing fetchrecursesubmodules option

We should not die when reading the submodule config cache since the user
might not be able to get out of that situation when the configuration is
part of the history.

We should handle this condition later when the value is about to be
used.

TODO: handle it with a die for all situations it was before
DONE: remove die from parse_fetch_recurse_submodules_arg