perf parse-events: Remove unused FILE input argument to scanner

perf parse-events: Remove unused FILE input argument to scanner

Now the events file isn't directly parsed from a FILE but stored in a
string prior to parsing, remove the FILE argument to the associated
scanner functions as they only ever pass NULL.

Tested-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Ian Rogers <irogers@google.com>
Tested-by: James Clark <james.clark@linaro.org>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>