AbstractFullNodeTest: Remove now empty test

JUnit4 would previously complain if there was not a single test
function, but doesn't anymore. Maybe because the class has a parent
class now.
SubscriptionManagerFCPTest: Start using AbstractFullNodeTest as base
class

- Strip down setUp() so it only initializes the FCP connection and
everything else is done at the member variables already, so the stuff is
less spaghetti.
- As a consequence, rename setUp() to setUpClient(). JUnit4 allows
arbitrary names because what is run before the test is determined by
"@Before", not by the function name.
- Use PluginRespirator.connecToOtherPlugin() instead of
FCPPluginClient.constructForUnitTest(): connectToOtherPlugin() is the
main API for obtaining FCP connections in real nodes, and we can use it
now since a PluginRespirator is available now due to the fact that the
parent class now creates a full Freenet node. It is always better to use
production code than special code paths for unit tests!
- The mFCPInterface variable was not used anymore, so it can be removed.
- Make the class final so unused variables are detected by the compiler
the next time.
- There are unrelated compiling failures remaining, the following
commits will fix them.
SubscriptionManagerFCPTest: Adapt to renaming of mWoT to mWebOfTrust

- This is due to the previous commit which changed the parent class to
be something else.
- I think member variables which are used by child classes should always
be self-explanatory, so I won't rename it in the parent class.