[libFuzzer] Disable handle-unstable.test for ARM and delete duplicated test file.

Summary:
This change should fix the failures mentioned in
https://reviews.llvm.org/D49684#1175245

Reviewers: kevinwkt, morehouse, metzman

Reviewed By: kevinwkt, morehouse

Subscribers: kristof.beyls, delcypher, chrib, #sanitizers, llvm-commits, kcc

Differential Revision: https://reviews.llvm.org/D49810

llvm-svn: 337949