* Remove version pin for java-diff-utils dependency
Latest version of the lib introduces a small behavior change/bug fix.
It no longer ignores empty lines. This actually makes sense.
Update the test data to reflect this change.
* Get rid of all remaining JUnit 4 usages except in prober & proxy subprojects
Caveat: Test suites aren't yet implemented in JUnit 5 so we still use the ones
from JUnit 5 in the core subproject.
* Fix some build errors
* Upgradle JUnit to 4.13
Removed third_party/junit folder and all usage of the
JunitBackPort class. As a result, third_party is no
longer a Gradle subproject.
Minor code changes were needed to work around an
error-prone pattern: multiple statement in assertThrows'
runnable lambda.
Also third_party/activation and third_party/jsch. These
dependencies are loaded from remote maven repo. The local
copies are not in use.
