perf vendor events: Drop incomplete multiple mapfile support

Currently jevents supports multiple mapfiles, but this is only in the
form where mapfile basename starts with 'mapfile.csv'

At the moment, no architectures actually use multiple mapfiles, so drop
the support for now.

This patch also solves a nuisance where, when the mapfile is edited and
the text editor may create a backup, jevents may use the backup, as
shown:

  jevents: Many mapfiles? Using pmu-events/arch/arm64/mapfile.csv~, ignoring pmu-events/arch/arm64/mapfile.csv

Signed-off-by: John Garry <john.garry@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Ganapatrao Kulkarni <ganapatrao.kulkarni@cavium.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: William Cohen <wcohen@redhat.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linuxarm@huawei.com
Link: http://lkml.kernel.org/r/1520506716-197429-2-git-send-email-john.garry@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>