perf jevents: If the long_desc and desc are identical then drop the long_desc

perf jevents: If the long_desc and desc are identical then drop the long_desc

If the short and long descriptions are the same then save space and
don't store both of them. When storing the desc in the perf_pmu_alias,
don't duplicate the desc into the long_desc.

By avoiding storing the duplicate the size of the events string in the
binary on x86 is reduced by 29,840 bytes.

Fix tests that expect a duplicated description.

Signed-off-by: Ian Rogers <irogers@google.com>
Link: https://lore.kernel.org/r/20250710235126.1086011-9-irogers@google.com
Signed-off-by: Namhyung Kim <namhyung@kernel.org>