Fix unused private $tz, add missing $utc private properties

[adrian-martinez-interactiv4]

In code constructor, $this->utc referenced a non-existing property; at the same time, a DateTimeZone private property $tz was declared but not used.

It seems property got renamed somewhere in time in code usage, but not in property declaration.

Provide a narrative description of what you are trying to accomplish:

• [x] Are you fixing a bug?

  • [x] Detail how the bug is invoked currently.
  • [x] Detail the original, incorrect behavior.
  • [x] Detail the new, expected behavior.
  • [x] Base your feature on the master branch, and submit against that branch.
  • [ ] Add a regression test that demonstrates the bug, and proves the fix.
  • [ ] Add a CHANGELOG.md entry for the fix.

• [ ] Are you creating a new feature?

  • [ ] Why is the new feature needed? What purpose does it serve?
  • [ ] How will users use the new feature?
  • [ ] Base your feature on the develop branch, and submit against that branch.
  • [ ] Add only one feature per pull request; split multiple features over multiple pull requests
  • [ ] Add tests for the new feature.
  • [ ] Add documentation for the new feature.
  • [ ] Add a CHANGELOG.md entry for the new feature.

• [ ] Is this related to quality assurance?

• [ ] Is this related to documentation?

[michalbundyra]

Thanks, @adrian-martinez-interactiv4!