perf expr: Fix memory leaks in metric bison

perf expr: Fix memory leaks in metric bison

Add a destructor for strings to reclaim memory in the event of errors.
Free the ID given for a lookup, it was previously strdup-ed in the lex
code.

Signed-off-by: Ian Rogers <irogers@google.com>
Reviewed-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lore.kernel.org/lkml/20200513000318.15166-1-irogers@google.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>