Spreadsheet: Remove cursor keys from is_navigation

This change allows for cursor navigation of a forumula while editing
rather than having to use the mouse to edit the cursor position within
a cell. Tab and Enter still allow you to navigate out of the cell to
next row or columns. :)

Userland/Applications/Spreadsheet/SpreadsheetView.h

@@ -40,10 +40,6 @@ private:
 
         switch (event.key()) {
         case KeyCode::Key_Tab:
-        case KeyCode::Key_Left:
-        case KeyCode::Key_Right:
-        case KeyCode::Key_Up:
-        case KeyCode::Key_Down:
         case KeyCode::Key_Return:
             return true;
         default: