Remove getPrimaryPhysicalDisplayId

SurfaceFlinger marks the first connected display as primary, which is
not really useful, and surfaceflinger should not care about this.

The display manager can decide whether a display is primary when needed.

Bug: 240703637
Test: atest surfaceflinger_test
Change-Id: Ia5368a137c689989fcac7b355d1c6dddf3a8cf26