memcg: get rid of swapaccount leftovers

The swapaccount kernel parameter without any values has been removed by
commit a2c8990aed ("memsw: remove noswapaccount kernel parameter") but
it seems that we didn't get rid of all the left overs.

Make sure that menuconfig help text and kernel-parameters.txt are clear
about value for the paramter and remove the stalled comment which is not
very much useful on its own.

Signed-off-by: Michal Hocko <mhocko@suse.cz>
Reported-by: Gergely Risko <gergely@risko.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/kernel-parameters.txt

@@ -2953,7 +2953,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			improve throughput, but will also increase the
 			amount of memory reserved for use by the client.
 
-	swapaccount[=0|1]
+	swapaccount=[0|1]
 			[KNL] Enable accounting of swap in memory resource
 			controller if no parameter or 1 is given or disable
 			it if 0 is given (See Documentation/cgroups/memory.txt)