gfs2: fix remote evict for read-only filesystems

gfs2: fix remote evict for read-only filesystems

When a node tries to delete an inode, it first requests exclusive access
to the iopen glock.  This triggers demote requests on all remote nodes
currently holding the iopen glock.  To satisfy those requests, the
remote nodes evict the inode in question, or they poke the corresponding
inode glock to signal that the inode is still in active use.

This behavior doesn't depend on whether or not a filesystem is
read-only, so remove the incorrect read-only check.

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>