Update jspsych-extension-mouse-tracking.html

[EitanHemed]

The const start has been removed in the previous commit, and does not seem to be currently required to run the demo (i.e., the reference to it raises "Uncaught ReferenceError:".

[changeset-bot]

⚠️ No Changeset found

Latest commit: 82ca149

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR

[jadeddelta]

thanks for the contribution @EitanHemed ! :) LGTM, just removed some additional code: the check for the jspsych object is only for online hosted examples but since these are locally hosted it is not necessary to have that check.