perf_counter tools: fix Documentation/perf_counter build error

Mike Galbraith reported:

> marge:..Documentation/perf_counter # make
>     CC builtin-stat.o
> In file included from builtin-stat.c:71:
> /usr/include/ctype.h:102: error: expected expression before ‘]’ token

Remove the ctype.h include.
Signed-off-by: NIngo Molnar <mingo@elte.hu>

Documentation/perf_counter/builtin-stat.c

@@ -68,7 +68,6 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <errno.h>
-#include <ctype.h>
 #include <time.h>
 #include <sched.h>
 #include <pthread.h>

Documentation/perf_counter/builtin-top.c

@@ -49,7 +49,6 @@
 #include <fcntl.h>
 #include <stdio.h>
 #include <errno.h>
-#include <ctype.h>
 #include <time.h>
 #include <sched.h>
 #include <pthread.h>