Remove unused and generated files from the benchmark; do not propagate such files from the bug-mining framework.

[rjust]

'build_files' associated with the buggy version are not used; both buggy and fixed use the build file of the fixed version. The additional build files are generated and only used during bug-mining.
They should be removed and no longer be propagated from the bug-mining scripts.

Similarly, test patches (in contrast to source patches) are not minimized and can be easily regenerated with git diff. These should be removed from the patches directory.