Fix implicit prepare method (must not be static)

Author: unp1

key.core/src/main/java/de/uka/ilkd/key/java/transformations/pipeline/CreateBuilder.java

@@ -74,7 +74,6 @@ private BlockStmt createBody() {
     public MethodDeclaration createMethod(TypeDeclaration<?> type) {
         NodeList<Modifier> modifiers = new NodeList<>();
         modifiers.add(new Modifier(Modifier.DefaultKeyword.PUBLIC));
-        modifiers.add(new Modifier(Modifier.DefaultKeyword.STATIC));
 
         MethodDeclaration md = new MethodDeclaration(
             modifiers, new ClassOrInterfaceType(null, services.getId(type)),