Remove limits on the number of fix-it hints and ranges in the DiagnosticsEngine.

Summary:
The limits on the number of fix-it hints and ranges attached to a
diagnostic are arbitrary and don't apply universally to all users of the
DiagnosticsEngine. The way the limits are enforced may lead to diagnostics
generating invalid sets of fixes. I suggest removing the limits, which will also
simplify the implementation.

Reviewers: rsmith

Reviewed By: rsmith

Subscribers: klimek, cfe-commits

Differential Revision: http://reviews.llvm.org/D3879