perf tools: Remove libtraceevent in .gitignore

The libtraceevent has been removed from the source tree, and .gitignore
needs to be updated as well.

Fixes: 4171925a ("tools lib traceevent: Remove libtraceevent")
Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
Link: https://lore.kernel.org/r/20250726111532.8031-1-cp0613@linux.alibaba.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>