Remove pre-3.0 compat code in FindAndModify

Since ext-mongodb 1.5.0 drops support for server 2.6, we can remove wire version checks and legacy code for servers before 3.0 (i.e. wire version 3).

Skip redundant error message checks, since their codes do not overlap with the three errors specifically excluded by the spec and all other server errors are resumable.

Deprecate the unused class constant, which can be removed in 2.0 (PHPLIB-360).

MongoDB\Driver\Exception\RuntimeException does not conflict in this file, so we can also remove its alias.

MongoDB 4.0 adds a "clusterTime" field to change stream documents. Rather than add conditional logic to expect this in tests, implement a new comparison function that fields not found in our expected document.

Fix monospace formatting in watch() docs

Fix reference to constants in Collection::watch() docs