Remove TimeValue usage from Core/Module

Summary:
The only interesting part here is that TimePoint and TimeValue have different
natural string representations, which affects "target modules list" output. It
is now "2016-07-09 04:02:21.000000000", whereas previously in was
"Sat Jul  9 04:02:21 2016". I wanted to check if we're OK with that.

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D26275

llvm-svn: 286349