#6159 Removing deprecated method in util class

[vaidikcode]

Description

As noted in #6159, I removed the getPluralFromKind(String kind) method along with its test. Additionally, I modified the dependency in kubernetes-client-api/src/main/java/io/fabric8/kubernetes/client/dsl/base/ResourceDefinitionContext.java, specifically in the protected void validate() method, to utilize HasMetadata.getPlural(kind.getClass()) instead of the getPluralFromKind(String kind) method.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change
• Chore (non-breaking change which doesn't affect codebase;
  test, version modification, documentation, etc.)

Checklist

• Code contributed by me aligns with current project license: Apache 2.0
• I Added CHANGELOG entry regarding this change
• I have implemented unit tests to cover my changes
• I have added/updated the javadocs and other documentation accordingly
• No new bugs, code smells, etc. in SonarCloud report
• I tested my code in Kubernetes
• I tested my code in OpenShift