exportUrlsToPortal: stop fusing remote urls

this proofs insanely troublesome. because of the way the filetransfer
portal works we need to open() paths before sending them to the portal,
this however means open() on our fuse-redirected paths which behind the
scenes is actually a remote stat() to determine the file type. this is
insanely expensive and just will not ever work for more than a couple of
files.

for the time being we'll disable fuse redirection unless explicitly
opted into via KCOREADDONS_FUSE_REDIRECT so it can still be tested.

CCBUG: 457529
(cherry picked from commit 9aea173c)