Usually, you need to terminate the list of command line options using a -- marker.
--
Try something like svn rm -- -.
svn rm -- -
Same if you want to remove the directory from the file system: rm -r -- -.
rm -r -- -
You could try svn rm ./-
svn rm ./-
It might not actually be a minus, tho', but a similar-looking character.
try svn rm -- -
-- means "stop reading options".