Remove redundant pageview segment.io events (ECOM-619)

[ECOM-619](https://openedx.atlassian.net/browse/ECOM-619)

Background:
* These pageview events were originally included as a workaround for MixPanel, which we're no longer using.
* On Oct 9, segment.io made a change to its API so that the "noninteraction" flag we are setting stopped working.  This resulted in a bounce rate of 0% in Google Analytics.

This PR removes the redundant events, which should improve page performance as well as fixing the bounce rate issue.

Reviewers: @rlucioni @stephensanchez