remove FILE* usage from SBStream.i

Summary:
This patch removes FILE* and replaces it with SBFile and FileSP the
SWIG interface for `SBStream.i`.   And this is the last one.   With
this change, nothing in the python API will can access a FILE* method
on the C++ side.

Reviewers: JDevlieghere, jasonmolenda, labath

Reviewed By: labath

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68960

llvm-svn: 374924