Remove redundant progress logging when verbose output is enabled

[joeltg]

Currently, when optimizing the final embedding with verbose = True, UMAP displays a tqdm progress bar ranging over the number of epochs, and also prints a completed {n} / {n_epochs} epochs message every 10 epochs. This leaves traces of the tqdm progress bar in stdout, like so:

By removing this, we just let tqdm do its thing, which displays all the same information with less cumulative clutter.

Fixes #1154