perf pmu: Remove perf_pmu_lex() needless declaration

perf pmu: Remove perf_pmu_lex() needless declaration

It builds without it, perhaps with some older combination of flex/bison
we needed this, clean it up a bit removing this.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
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: https://lore.kernel.org/r/20220909044542.1087870-3-cuigaosheng1@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>