perf inject: Remove unused 'input_name' static var

perf inject: Remove unused 'input_name' static var

If we ever want to allow inject to work with something other than stdin,
we can put it back, but so far it is completely unused, so ditch it.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-qmwpnktckhd43eynnkxgqfpm@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>