the slime-tramp contrib should not list tramp as a :slime-dependencies.

While i'm not 100% sure i'm using the :slime-dependencies contrib, this patch makes slime-tramp work (otherwise it signals an error at startup saying tramp-init is not defined (which it isn't of course)).

i have no idea how slime should behave if the slime-tramp contrib is loaded and tramp isn't available (is tramp ever unavailable?)