Shave a stack frame off asserts.

No-one cares about seeing "async_safe_fatal" (which you have to admit is a
pretty confusing name for an app developer anyway).

On arm:

     #00 pc 0001a43c  /system/lib/libc.so (abort+63)
     #01 pc 0001a627  /system/lib/libc.so (__assert+14)

And aarch64:

     #00 pc 000000000001d75c  /system/lib64/libc.so (abort+120)
     #01 pc 000000000001dad0  /system/lib64/libc.so (__assert+44)

Bug: N/A
Test: ran `crasher assert` and `crasher64 assert`
Change-Id: I00be71c566c74cdb00f8e95d634777155bc3da03