Remove '.' print in tools/js_optimizer.py. Fixes other.test_chunking on Windows.

On Windows, prints to stdout/stderr do not appear coherently synchronized per-line if multiple threads print data simultaneously to console. This caused other.test_chunking tests to fail when they receive output like

emcc:    step took 5.09 seconds
emcc: running pre-closure post-opts
emcc: running post-closure post-opts
emcc: applying js optimization passes: ['eliminate', 'simplifyExpressionsPre', 'simplifyExpressionsPost', 'last']
splitting up js o.
ptimization into 2 chunks of size 1048576, using 2 cores  (total: 1.42 MB)
emcc:    step took 2.37 seconds
emcc: total time: 11.75 seconds

where the test looks for the string 'splitting up js optimization into' from the output. Note that the chunk processor thread has printed a single '.' in between the critical line, creating a race condition that randomly makes the test pass or fail, depending on where in the output the '.' lands in.