Revert "Use lowered resource kind as file name"

This reverts commit aaba479.

pkg/model/file/mixins.go

@@ -17,8 +17,6 @@ limitations under the License.
 package file
 
 import (
-	"strings"
-
 	"sigs.k8s.io/kubebuilder/v2/pkg/model/resource"
 )
 
@@ -132,15 +130,13 @@ func (m *BoilerplateMixin) InjectBoilerplate(boilerplate string) {
 
 // ResourceMixin provides templates with a injectable resource field
 type ResourceMixin struct {
-	Resource            *resource.Resource
-	LoweredResourceKind string
+	Resource *resource.Resource
 }
 
 // InjectResource implements HasResource
 func (m *ResourceMixin) InjectResource(res *resource.Resource) {
 	if m.Resource == nil {
 		m.Resource = res
-		m.LoweredResourceKind = strings.ToLower(res.Kind)
 	}
 }