Remove unnecessary equals and hashcode tests

[51-code]

Fixes #33 .

Coverity flagged an equality test in ImmutableMapTest.java because of an unnecessary method call. Removing just that line makes the equality test quite unnecessary itself as the function call was there to check for side-effects.

My thought process here:

1. Remove the line of code.
2. Remove the whole test as it's useless now. There is equalsverifier tests anyway!
3. Why not remove all manual equals tests to remove clutter, equalsverifier tool is used anyway.

Added bonus:
Coverity won't flag other tests in the future, because many other equality tests had similar unnecessary function calls but for some reason they were not flagged yet.

TLDR:
Equalsverifier is used in the project, so manual equality tests are not necessary. Coverity had flagged one of the manual tests, might flag more later.

[Tiihott]

As EqualsVerifier tests the equals() and hashCode() automatically with a single line, the manual tests become redundant and they should be fine to remove when the EqualsVerifier tests are implemented properly.
LGTM