Documentation: get rid of write_super

The '->write_super' superblock method is gone, and this patch removes all the
references to 'write_super' from various pieces of the kernel documentation.

Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

Documentation/filesystems/porting

@@ -94,9 +94,8 @@ protected.
 ---
 [mandatory]
 
-BKL is also moved from around sb operations.  ->write_super() Is now called 
-without BKL held.  BKL should have been shifted into individual fs sb_op
-functions.  If you don't need it, remove it.  
+BKL is also moved from around sb operations. BKL should have been shifted into
+individual fs sb_op functions.  If you don't need it, remove it.
 
 ---
 [informational]