[Shortcut Helper] Updated system shortcuts

+ Removed Meta + Enter from go to home screen shortcut
+ Removed Meta + Backspace from Go back shortcut

Test: Manual - open shortcut helper, ensure the shortcuts listed above
don't show up
Flag: EXEMPT Trivial fix
Fix: 370923953
Fix: 370928529

Change-Id: Ib4694ed5d3e1899e03435459aad76919a303dd58