Remove FDE warning from AccessibilityShortcutChooserActivity

This encryption warning is never shown, since
StorageManager.isNonDefaultBlockEncrypted() is hard-coded to return
false, since FDE (Full Disk Encryption) is no longer supported.
Therefore, remove an unused TextView and string, and stop calling
StorageManager.isNonDefaultBlockEncrypted().

Remove the word "encryption" from the layout name
"accessibility_enable_service_encryption_warning", since this layout
is still used for other, non-encryption related warnings.

Bug: 208476087
Change-Id: Ic4e9024eadd602205516aa3ba4cc01887a2a7d34