As you can see in this image there is an "Applications" button which I want to remove.
I am using Ubuntu 18.04.
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Open Terminal and run
This should launch a GUI window which lets you manage your installed GNOME shell extensions. Disable (toggle off) "Applications Menu" extension from there and relogin.
If you are not able to turn that off/on then you should check whether you have turned on Hot corners in Gnome Tweak tool then follow this step.