AbstractProcessStep: De-virtualize finish() method

Provide a setDoneHook() setter instead. The hook is
introduced temporarily, as when all the subclasses
are transformed to use the task tree, the done hook
is going to be a part of the subclass' recipe.

Task-number: QTCREATORBUG-29168
Change-Id: Idbc0f8b8a32c8df2fa5ecb73ed1cbaedad99620d
Reviewed-by: hjk <hjk@qt.io>

src/plugins/cmakeprojectmanager/cmakebuildstep.h

@@ -77,7 +77,6 @@ signals:
 private:
     Utils::CommandLine cmakeCommand() const;
 
-    void finish(Utils::ProcessResult result) override;
     bool fromMap(const QVariantMap &map) override;
 
     bool init() override;