nemo-desktop-link.c: Don't allow an attempt to rename mounts.

It's not currently implemented, and is disallowed correctly in other
places (as well as the context menu.  This only affects F2).

Fixes linuxmint#2169

nemo-desktop-link.c: Don't allow an attempt to rename mounts.

It's not currently implemented, and is disallowed correctly in other
places (as well as the context menu.  This only affects F2).

Fixes linuxmint#2169