tests(ngMock): remove a broken jqLite cache clearing (#16515)

This commit removes the resetting of `angular.element.cache` in some tests;
this was desynchronizing jqLite.cache & the local jqCache variable and since
some parts of the code use one of them and some the other one, it was breaking
JQLite._data. `angular.element.cache` doesn't even exist when jQuery 2+ is used.

Closes #16515
Refs #16512