Lint/style fixes and removal of unused code

* Remove SpinLock, Condition Variable and Thread wrappers from SyncUtils (unused)
* Remove unused TrackingCollector
* Reformat code to not go over 100 columns except in rare cases
* Fix up a lot of whitespace/indentation errors (using cpplint.py)
* Remove empty JavaDoc @param/@return annotations
* Remove some blocks of commented-out code
* Remove DynamicBuffer (unused)
* Remove support for native combiners
  (Java-side support was already removed, not covered by any tests)
* Remove object factory support and interfaces for for native implementations
  of Partitioner, Input/Output formats, etc (dead code)
* Remove cityhash and wrapper (unused)
* Remove BufferedInputStream/BufferedOutputStream
* Remove some unused constants from Constants.java
* Remove some commented-out code in TestSort.cc