perf kmem: Fix breakage introduced by 5a0e3ad6 slab.h script

Commit 5a0e3ad6 ("include cleanup: Update gfp.h and slab.h
includes to prepare for breaking implicit slab.h inclusion
from percpu.h") added a '#include <linux/slab.h>' to
tools/perf/builtin-kmem.h because: that tool has lines like
this:

        if (!strcmp(event->name, "kmalloc") ||
            !strcmp(event->name, "kmem_cache_alloc")) {
                process_alloc_event(data, event, cpu, timestamp, thread, 0);
                return;
        }

So, using the script regex:

>>> import re
>>> s = re.compile(r'^(|.*[^a-zA-Z0-9_])_*(slab_is_available|kmem_cache_|k[mzc]alloc|krealloc|kz?free|ksize|__getname|putname)')
>>> l = '   !strcmp(event->name, "kmem_cache_alloc")) {'
>>> s.search(l)
<_sre.SRE_Match object at 0xb77b1ad0>
>>>

Remove that file that is not available in the tools/perf include
path and thus builtin-kmem.c couldn't be compiled.

Reported-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc...