test_fib.py: Remove empty methods

 test_fib.py: Remove empty methods

Remove methods that only call super.

py27 runtests: commands[5] | stestr --test-path ./test run --slowest test_fib
==============================================================================
FIB Test Case
==============================================================================
==============================================================================
IPv6 Test Case
==============================================================================
12:19:23,856 Couldn't stat : /tmp/vpp-unittest-TestFIB-BcLbkQ/stats.sock
{1} test.test_fib.TestFIB.test_fib [0.216340s] ... ok
==============================================================================
IPv4 Test Case
==============================================================================
{0} test.test_ip6.TestIPv6.test_fib [5.328127s] ... ok
12:19:33,921 Couldn't stat : /tmp/vpp-unittest-TestIPv4-AoGvoK/stats.sock
{1} test.test_ip4.TestIPv4.test_fib [5.071083s] ... ok

======
Totals
======
Ran: 3 tests in 34.0000 sec.
 - Passed: 3
 - Skipped: 0
 - Expected Fail: 0
 - Unexpected Success: 0
 - Failed: 0
Sum of execute time for each test: 10.6155 sec.

==============
Worker Balance
==============
 - Worker 0 (1 tests) => 0:00:05.328127
 - Worker 1 (2 tests) => 0:00:10.251002
Test id                          Runtime (s)
-------------------------------  -----------
test.test_ip6.TestIPv6.test_fib  5.328
test.test_ip4.TestIPv4.test_fib  5.071
test.test_fib.TestFIB.test_fib   0.216
______________________________________________________ summary ______________________________________________________
  py27: commands succeeded
  congratulations :)
vagrant@vpp:/vpp$

Change-Id: Ia07fe13affe2672ea2df774678312c6db8ea63fb
Signed-off-by: Paul Vinciguerra <pvinci@vinciconsulting.com>