perf tools: Remove unused test-volatile-register-var.c

Since commit 01287e2c

, test-volatile-register-var.c is no more built
as part of the automatic feature check.

This patch remove the unneeded file.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/339d86ad76741ed929defd18541f774b404003b4.1389461371.git.ydroneaud@opteya.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>