Cleanup openapi template overrides for 6.3.0

- Remove the client generator pojo.mustache override file since the
  bug we worked around has been fixed in 6.3.0.
  (OpenAPITools/openapi-generator#12630)
- Remove the server generator pojo.mustache override file since the
  bug we worked around has been fixed in 6.3.0.
  (OpenAPITools/openapi-generator#13076)
- Merge in some upstream changes for the server generator
  api.mustache override file that were added in 6.3.0.

buildSrc/src/main/resources/templates/api.mustache

@@ -3,8 +3,8 @@ package {{package}};
 {{#imports}}import {{import}};
 {{/imports}}
 
-import javax.ws.rs.*;
-import javax.ws.rs.core.Response;
+import {{javaxPackage}}.ws.rs.*;
+import {{javaxPackage}}.ws.rs.core.Response;
 
 {{#useSwaggerAnnotations}}
 import io.swagger.annotations.*;
@@ -17,8 +17,8 @@ import java.util.concurrent.CompletableFuture;
 import org.jboss.resteasy.plugins.providers.multipart.MultipartInput;
 import java.util.Map;
 import java.util.List;
-{{#useBeanValidation}}import javax.validation.constraints.*;
-import javax.validation.Valid;{{/useBeanValidation}}
+{{#useBeanValidation}}import {{javaxPackage}}.validation.constraints.*;
+import {{javaxPackage}}.validation.Valid;{{/useBeanValidation}}
 
 @Path("{{commonPath}}"){{#useSwaggerAnnotations}}
 @Api(description = "the {{{baseName}}} API"){{/useSwaggerAnnotations}}{{#hasConsumes}}

client/build.gradle

@@ -38,7 +38,6 @@ openApiGenerate {
     configOptions = [
         dateLibrary: "java8"
     ]
-    templateDir = "$rootDir/client/buildSrc/src/main/resources/templates"
     modelPackage = "org.candlepin.dto.api.client.v1"
     apiPackage = "org.candlepin.resource.client.v1"
     invokerPackage = "org.candlepin.invoker.client"