Revert "minidump: Add ability to attach (breakpad) symbol files to placeholder modules"

This reverts r354263, because it uncovered a problem in handling of the
minidumps with conflicting UUIDs. If a minidump contains two files with
the same UUID, we will not create to placeholder modules for them, but
instead reuse the first one for the second instance. This creates a
problem because these modules have their load address hardcoded in them
(and I've added an assert to verify that).

Technically this is not a problem with this patch, as the same issue
existed in the previous implementation, but it did not have the assert
which would diagnose that. Nonetheless, I am reverting this until I
figure out what's the best course of action in this situation.

llvm-svn: 354324