Fix severity of analyzer warnings; add new warnings.

* The following were high severity warnings but mistakenly
  grouped into analyzer warnings in a recent change.
        clang-analyzer-unix.Malloc
        clang-analyzer-cplusplus.NewDeleteLeaks
        clang-analyzer-cplusplus.NewDelete
* Add new Protoc and Kotlin warnings about unused imports and variables.

Bug: 141493530
Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Change-Id: Ied1f9ace97f29fba58a40dff2346a0391ab22f06