Remove Access emoji and Access voice typing shortcuts

1. These two shortcuts (Access emoji and Access voice typing) will be handed by Gboard, so it won't work if the current IME is not Gboard. So basically these two shortcuts should not be hardcoded in the UI.
2. Because Gboard can't receive shortcuts with meta modifier, we decided to change these two shortcuts to use alt modifier. And we may change these two shortcuts to other key combinations in future. So it's better to let Gboard (the current IME) provide their shortcuts and show them here.

screenshot: https://screenshot.googleplex.com/9xG8sWafduQGuHA.png

Bug: 259352579
Test: manual
Change-Id: I132ddac876de5afd208e24adc410ae4d1f91a7f0