GuiRobot: Remove push(KeyCodeCombination)
GuiRobot: Remove push(KeyCodeCombination)

GuiRobot#push(KeyCodeCombination) is not used in the codebase.

Let's remove it.

CS2103R-Eugene-Peh/addressbook-level4,damithc/addressbook-level4,damithc/addressbook-level4,damithc/addressbook-level4,CS2103R-Eugene-Peh/addressbook-level4,se-edu/addressbook-level3,CS2103R-Eugene-Peh/addressbook-level4