Remove asciidoc plugin.

No longer required.

See #3044

Author: mp911de

pom.xml

@@ -339,10 +339,6 @@
 				<groupId>org.apache.maven.plugins</groupId>
 				<artifactId>maven-assembly-plugin</artifactId>
 			</plugin>
-			<plugin>
-				<groupId>org.asciidoctor</groupId>
-				<artifactId>asciidoctor-maven-plugin</artifactId>
-			</plugin>
 			<plugin>
 				<groupId>io.spring.maven.antora</groupId>
 				<artifactId>antora-maven-plugin</artifactId>