Removing app from download queue in Amazon App Store
Go to My apps-> cloud-> hold the app you want to remove (it is valid only for installed or downloaded apps not for paused ore ongoing download). 

If you want to remove ongoing download, then you must cancel that. To cancel, you have to go to setting-> running apps-> amazon app store.

You will see 4-6 processes there. You have to stop download process from there. Note: the download process will only appear if that download is running at that time and it may take a few seconds to appear. 

After stopping download process, when you will return to that app in app store's cloud section, you will see download cancelled. Now you can hold that entry and safely choose remove from upcoming box.