CiviUnitTestCase - Remove redundant reset

CiviUnitTestCase - Remove redundant reset

In CiviUnitTestCase, there are methods `setUpBeforeClass()` and `setUp()`.
Both methods reset the database unconditionally.

The general flow is like this:

  1: setUpBeforeClass();
  2: setUp(); testApple(); tearDown();
  3: setUp(); testBanana(); tearDown();
  4: setUp(); testCherry(); tearDown();
  5: tearDownAfterClass();

You might say: "Aha!  You need the call in `setUp`, because it runs more
frequently!" But not really - because `setUp()` has an extra guard
(`static::$dbInit`).  In effect, you perform DB-reset at step 1 -- and then
immediately again on step 2 -- and then never again (steps 3+4+5).

It is conceivable that a subclass might override these methods and inject
additional initialization steps -- in which case, this patch may affect
their behavior. We'll just have to run the test-suite to find out.

Final thought - If `static::$dbInit` were manipulated by other code, then
`setUp()` would be much more interesting.  But it's counterfactual -- grep
finds nothing that manipulates `dbInit`.