Remove internal display related methods

SurfaceFlinger and SurfaceComposerClient simply return the first
connected display as internal display, which is not really correct.
In particular,in the case of dual display for foldable devices, both
displays are marked as Internal determined by calling into HWC2
IComposerClient::getDisplayConnectionType().

Therefore, the concept of internal/external/primary displays is removed
from SurfaceFlinger, and the display manager is the better place to
handle the logics.

flatland is modified to take an extra argument to specify display id,
and error occurs if no display is specified in case of multi-display.

Bug: 241285477
Bug: 242763577
Bug: 74619554
Test: atest libgui_test libsurfaceflinger_unittest SurfaceFlinger_test
Change-Id: Ib6c7e502ef3269c2c60a4e5388e5ac75275f87ed