[crashlog] Change heuristic to stripping the meta data from crashlogs

Instead trying to pro-actively determine if the first line in a
crashlog contains meta data, change the heuristic to do the following:

 1. To trying to parse the whole file. If that fails, then:
 2. Strip the first line and try parsing the remainder of the file. If
    that fails, then:
 3. Fall back to the textual crashlog parser.

rdar://88580543

Differential revision: https://reviews.llvm.org/D119755