[libFuzzer] Remove unstable edge handling

Summary:
Remove code for handling unstable edges from libFuzzer since
it has not been found useful.

Differential Revision: https://reviews.llvm.org/D56730

llvm-svn: 351262
GitOrigin-RevId: 9e14cccf6fe5827b92b6814ec1ee193b8bcd99b9
8 files changed