Revert "Disable browser_tests and unit_tests for now, they require unavailable mock4js"

This reverts commit 0d9fef72ec07cd60a9c7c52fe61c5346d1cc3119.

mock4js is now excluded from deletion in Makefile.
Do not prune mock4js, it is used by some unittests and not available
elsewhere in the Ports Tree.