Remove IntervalTimer class

Summary:
it was added back in 2013, but there are no uses of it. I started refactoring
it, but then it occured to me it would better to delete it.

Reviewers: clayborg, zturner

Subscribers: lldb-commits

Differential Revision: https://reviews.llvm.org/D25393

llvm-svn: 284599
1 file changed