mediaextractor: ignore platform's profiler assist signal

Due to security constraints, platform profilers that do remote stack
unwinding need the target process' cooperation. This is implemented via
a bionic signal handler.

On debug builds, media extractor can end up being targeted by such
system-wide profiling, which can crash the process due to
seccomp/minijail (specifically, due to sendmsg that is used for sending
file descriptors over a unix socket).

Tested: synced updated binary to crosshatch-userdebug, confirmed that
        sending signal 36 with si_val 1 doesn't crash mediaextractor.
Bug: 149328505
Change-Id: Idf34e08edf99a82c72146aebeb5e46e5cf5af2f3