Remove F_modify flag from FileOutputBuffer.

This code is dead. There is no use of the feature in the entire LLVM codebase.

Differential Revision: https://reviews.llvm.org/D56939

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351613 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed