Remove CodeGenerator API

It was an early exploratory attempt at code generation, and not
currently in use by the system anywhere. It will be done differently.

As this removes API, it is a breaking change.

Author: ctrueden

pom.xml

@@ -10,7 +10,7 @@
 	</parent>
 
 	<artifactId>scijava-common</artifactId>
-	<version>2.28.2-SNAPSHOT</version>
+	<version>3.0.0-SNAPSHOT</version>
 
 	<name>SciJava Common</name>
 	<description>SciJava Common is a shared library for SciJava software. It provides a plugin framework, with an extensible mechanism for service discovery, backed by its own annotation processor, so that plugins can be loaded dynamically. It is used by both ImageJ and SCIFIO.</description>