floss: Remove the TARGET_FLOSS that are used for enabling Aflags

Before Aflags are supported on ChromeOS, we use TARGET_FLOSS to enable
them. Now we are able to enable through aflags.conf and remove the
TARGET_FLOSS.

NOTE: Merge this after https://crrev.com/c/5524439 and
      https://r.android.com/3071603

Bug: 339340027
Tag: #floss
Test: mmm packages/modules/Bluetooth
Flag: EXEMPT, Floss-only changes
Change-Id: I3579b6cf66f551e10078b4b5a8100497a0901c76