GH-110 - Remove obsolete plugin repository declaration.

It was only used to access the Spring Asciidoctor Backends, but starting with version 0.0.4, the JAR is available from Maven Central.

Author: odrotbohm

pom.xml

@@ -579,21 +579,4 @@ limitations under the License.
 		</repository>
 	</repositories>
 
-	<pluginRepositories>
-		<pluginRepository>
-			<id>spring-plugins-release</id>
-			<url>https://repo.spring.io/plugins-release</url>
-			<snapshots>
-				<enabled>false</enabled>
-			</snapshots>
-		</pluginRepository>
-		<pluginRepository>
-			<id>spring-plugins-snaposhot</id>
-			<url>https://repo.spring.io/plugins-snapshot</url>
-			<releases>
-				<enabled>false</enabled>
-			</releases>
-		</pluginRepository>
-	</pluginRepositories>
-
 </project>