Adds BSD and Apache-2 license metadata, which is being used by some of
the source files. All licenses are still of "notice" classification so
this doesn't change code distribution requirements.

Also removes contrib/ patches for consistency, which are only used as
example code but don't fall under these licenses.

Bug: 170111993
Test: libavb_host_unittest
Change-Id: I632ec11558241a172c013d423b0a46fcb0e85bd7