remove a smattering of isolated, unnecessary uses of FILE*

Summary:
There a a few call sites that use FILE* which are easy to
fix without disrupting anything else.

Reviewers: JDevlieghere, jasonmolenda, labath

Reviewed By: JDevlieghere, labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68444