Tests: Make ConfirmRemoveStudentDialogTest Enzyme-3 ready

[islemaster]

Following these instructions and reviewing this list I'm fixing up a few more tests to be ready for the Enzyme 3 upgrade.

I believe these are fixed in a backwards-compatible way; letting Drone confirm that.

Note: Diff best viewed ignoring whitespace.

[maddiedierker]

code changes look good! out of curiosity, is there a reason you updated expect statements to use assert instead?

[islemaster]

I switched because you can assert(true) but you have to expect(true).to.be.true. The former seems like the more expressive way to use enzyme helpers now that we're moving away from chai-enzyme. For example:

// Before, with chai-enzyme
expect(wrapper).to.containMatchingElement(...);

// BDD-style without chai-enzyme
expect(wrapper.containsMatchingElement(...)).to.be.true;

// I prefer assert-style here:
assert(wrapper.containsMatchingElement(...));

(Testing: If you assert(false); your test will fail, but if you expect(false); it will pass!)