You could try this: Open your gnome-shell, type keyboard layout and open it up. There should be three tabs in this window. Click the one on the right that says "Layouts." Click the "Options" button in the bottom-right corner of the window. You should see a list with the entries preceded by arrows. The third one down says "Alt/Win key behavior." Click this and it will drop down a list of options. The second-to-last option is "Meta is mapped to left Win key." Choose this one, close out the layouts menu, and it should be disabled.