How to remove “get info” sidebar in a finder window

I found this app BetterTouchTool. It lets me define a keyboard shortcut to maximize a window fully, without leaving black spaces on either sides.

1. Download app and open preferences by clicking its icon (boxed index finger) in the menu bar at the top of your screen.
2. Select 'Keyboard' tab
3. Select 'Global' in Applications on right
4. Finally choose Keyboard shortcut and Predefined Action.

I chose the following keyboard shortcuts, which I found safest and non overlapping:

1. Control ↑ Maximize Window
2. Control ← Maximize Window Left
3. Control → Maximize Window Right
4. Control ↓ Maximize window to bottom half

It's possible that there has been some corruption to that folder's .DS_Store file, which the Finder uses to remember it displayed that folder last time.

You'll probably want to check out Consequences of deleting .DS_Store before you actually delete it so you know what to expect.

1. Make sure the Finder doesn't have the relevant folder open.
2. Open Terminal.app in /Applications/Utilities.
3. Type cd followed by a space.
4. Drag the icon for the folder with the issues into the Terminal to automatically fill in the full path to that folder, and press enter.
5. Enter rm .DS_Store.
6. You might need to Relaunch the Finder.