jsterm-911456: Fix review comments

Signed-off-by: Joe Walker <jwalker@mozilla.com>
vkenter-969247:  Get rid of NS_VK_ENTER and nsIDOMKeyEvent::DOM_VK_ENTER

Change made in Mozilla source. See
https://bugzilla.mozilla.org/show_bug.cgi?id=969247

Signed-off-by: Joe Walker <jwalker@mozilla.com>