SurfaceFlinger: Remove NativeWindowSurface abstraction

This abstraction is only used to support some unnecessary white-box
test mocks that don't provide a ton of value for their fragility and
infrastructural cost.

BYPASS_IGBP_IGBC_API_REASON=wb work

Bug: 340933138
Flag: EXEMPT PURE_REFACTOR
Test: atest
Change-Id: Ie065a06ab13bb29e69814ce9299f6952a6664bca