Prevent auxiliary grammars from generating lexers

- A misconfiguration of Antlr4 produced an auxiliary gramma
   (UnicodeClasses), that was imported into the main kotlin grammar,
   to produce it's own Lexer, which was never used.
 - We no longer produce that Lexer, properly moving imports to the
   standard directory for that.
 - We manually copy a generated version for API compatibility, flagging
   it as both Generated and Deprecated for removal in PMD 8

pmd-kotlin/pom.xml

@@ -26,9 +26,6 @@
             <plugin>
                 <groupId>org.antlr</groupId>
                 <artifactId>antlr4-maven-plugin</artifactId>
-                <configuration combine.self="override">
-                    <libDirectory>src/main/antlr4/net/sourceforge/pmd/lang/kotlin/ast</libDirectory>
-                </configuration>
             </plugin>
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>