Previously, Hibernate Validator would fail to initialize if it was
on the classpath but an EL implementation was not.
OnValidatorAvailableCondition protected against this scenario by
initializing the validator.

The Hibernate Validator shortcoming was addressed in eb222209
(gh-7598). As a result, checking for the precences of the
ValidationProvider META-INF/services resource is now sufficient to
auto-configure validation. This commit removes
OnValidatorAvailableCondition as it is no longer necessary.

Closes gh-8110