Update HaveWriter specs.

- Remove the functionality checking the value of `:property` after
`:property=` has been invoked.

Current spec status:
- 2.0: 346 examples, 0 failures in 0.10908 seconds.
- 2.1: 412 examples, 0 failures in 0.10846 seconds.
Update HaveProperty specs.

Current spec status:
- 2.0: 370 examples, 0 failures in 0.10616 seconds.
- 2.1: 436 examples, 0 failures in 0.11945 seconds.