ext4: remove pointless sb_rdonly() checks from freezing code

ext4_freeze() and ext4_unfreeze() checks for sb_rdonly(). However this
check is pointless as VFS already checks for read-only filesystem before
calling filesystem specific methods. Remove the pointless checks.

Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230616165109.21695-1-jack@suse.cz


Signed-off-by: Theodore Ts'o <tytso@mit.edu>