Delete old REST test coverage: (Read|Create|Update|Delete)Test, deprecate RESTTestBase

Havin rolled this patch, I couldn't help but notice that:

1. \Drupal\rest\Tests\AuthTest is also completely incorporated by #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, so deleted that too
2. \Drupal\rest\Tests\CsrfTest is also completely incorporated by #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, so deleted that too
3. \Drupal\rest\Tests\NodeTest is mostly incorporated by #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, so deleted the parts that have been incorporated
4. \Drupal\rest\Tests\PageCacheTest is mostly incorporated by #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, if we just add some cache tag test coverage to #2737719, we can delete that too

Working on points 3 and 4 over in that other issue.

Addressed point 4 at #2737719-113: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, so rerolling this patch to also remove PageCacheTest.

Addressed point 3 at #2737719-114: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, so rerolling this patch to also remove NodeTest. In doing so, I discovered #2824827: \Drupal\hal\Normalizer\ContentEntityNormalizer::denormalize() fails with fatal PHP error when bundles are missing from link relation types, which again shows why we need to test all edge cases against all formats.

+1! Will do that in this patch too.

1. Can't remove \Drupal\hal\Tests\FileDenormalizeTest + \Drupal\Tests\hal\Kernel\FileNormalizeTest because adding File entity test coverage is not done by #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, that's for #2824572: Write EntityResourceTestBase subclasses for every other entity type. to add.
2. \Drupal\Tests\hal\Kernel\DenormalizeTest is testing edge cases for "type" link handling. All other test methods (the majority) can be removed. Although I think it's better to keep its testMarkFieldForDeletion() method too, that's explicit test coverage for an edge case, where #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method only added implicit test coverage for that. We should eventually move that into \Drupal\Tests\rest\Functional\EntityResource\EntityResourceTestBase too, but that'd make #2737719 even biggger, so I think it's fine to defer that to a follow-up.
3. \Drupal\Tests\hal\Kernel\EntityNormalizeTest tests a subset of #2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method, removed completely
4. \Drupal\Tests\hal\Kernel\EntityTranslationNormalizeTest + \Drupal\Tests\hal\Kernel\NormalizeTest are testing translation support, which actually is not properly supported at all yet, for that we have #2135829: [PP-1] EntityResource: translations support

#2737719: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method landed!

Let's see if this patch still applies.

Will roll a separate 8.3.x patch first thing tomorrow.

There were two changes in 8.3.x that prevented the patch from applying to 8.3.x too:

1. #1841474: Convert REST tests to Guzzle (would also help with core moving from WTB to BTB) already being committed to 8.3.x but not 8.2.x
2. the same thing I encountered at #2737719-134: EntityResource: Provide comprehensive test coverage: for every entity type, every format, every method.3:

3. The status field of Comment entities is validated before other fields in 8.3.x, due to [#2810381.

Reuploading the same 8.2.x patch as in #7, and a separate patch for 8.3.x.

Yay!