Shortcuts a11y - Simplify access with double-tap

Previously, double-tap would do nothing and just tell the user
to double-tap and hold to long press to activate. This isn't
necessary. Long press was only added for falsing, and is not
required when using talkback.

Fixes: 383245582
Test: atest KeyguardQuickAffordanceInteractorTest
Flag: EXEMPT bugfix
Change-Id: I0df3cc7424e145935dc2665f98b37bc5a972b102