LLDB: Use LLVM's type for minidump ExceptionStream [NFC]

Summary: The types defined for it in LLDB are now redundant with core types.

Reviewers: labath, clayborg

Reviewed By: clayborg

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68658

llvm-svn: 375243