Answer: Since your wimpy boss has abdicated his responsibilities, you need to develop your own plan, then tell him what you intend to do.
For example: “I’m glad to help with difficult issues, but people keep coming to me with simple things. I plan to show them how to solve these problems, and then I expect them to work independently. I would appreciate your support on this.”
Ask your manager to approve the list of problems that you plan to delegate. Explain the new strategy to your co-workers, then teach them what they need to know. If possible, provide written instructions for future reference.
After that, you must resist any temptation to succumb to their continued pleas for assistance. If you consistently encourage them to seek their own solutions, your dependent colleagues will eventually learn to fly solo.
If you need to have a difficult conversation with your coworkers, here are some suggestions: How to Give Feedback without Criticism.