perf kvm: Make function only used by 'perf kvm' static

No need to have this polluting util.h, it was polluted enough already.

Link: http://lkml.kernel.org/n/tip-wfdidqlwbvi5y0s61kv6z2gn@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/util.h

@@ -100,7 +100,6 @@ int perf_event_paranoid(void);
 void mem_bswap_64(void *src, int byte_size);
 void mem_bswap_32(void *src, int byte_size);
 
-const char *get_filename_for_perf_kvm(void);
 bool find_process(const char *name);
 
 #ifdef HAVE_ZLIB_SUPPORT