remove election_timing.js (and lib/election_timing_test.js)

Since disabling the timing checks in SERVER-26142, election_timing.js is reduced to a series of test cases that trigger elections by stepping down or stopping the primary under various election configurations (protocol version 0 or 1).

A typical election_timing.js test run typically takes longer than 10 minutes which is a little excessive compared to existing replica set tests.

This makes election_timing.js redundant with existing C++ unit tests and JS tests in jstests/replsets.