[analyzer] SATestBuild.py: Remove html and log when producing reference results.

The html reports are huge -- every issue in a given file results in a separate
copy of the source code, in HTML form, for the file. This gets very large
quickly and it doesn't make sense to check this into a reference repository.
Also remove the log when generating reference results because it can leak
absolute path names. We still keep both the html and the log around when
producing non-reference results.

llvm-svn: 258594