SF: Remove obsolete HWComposer members

Remove mExternalHwcDisplayId, an obsolete special case for legacy multi-
display mode. Assert primary display existence instead of propagating to
callers, which is closer to how headless mode would work, i.e. injecting
a placeholder primary display. Remove isVirtual checks now that they are
enforced at compile time. Prevent primary display disconnection for now.

Bug: 182939859
Test: libsurfaceflinger_unittest
Change-Id: I507db6a3ac0bda93005a86b38cca6ebbcd5c0155
diff --git a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
index 56ae414..e036f4d 100644
--- a/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
+++ b/services/surfaceflinger/tests/unittests/TestableSurfaceFlinger.h
@@ -439,8 +439,7 @@
 
     auto& mutableHwcDisplayData() { return getHwComposer().mDisplayData; }
     auto& mutableHwcPhysicalDisplayIdMap() { return getHwComposer().mPhysicalDisplayIdMap; }
-    auto& mutableInternalHwcDisplayId() { return getHwComposer().mInternalHwcDisplayId; }
-    auto& mutableExternalHwcDisplayId() { return getHwComposer().mExternalHwcDisplayId; }
+    auto& mutablePrimaryHwcDisplayId() { return getHwComposer().mPrimaryHwcDisplayId; }
     auto& mutableUseFrameRateApi() { return mFlinger->useFrameRateApi; }
 
     auto fromHandle(const sp<IBinder>& handle) {
@@ -600,13 +599,12 @@
                 LOG_ALWAYS_FATAL_IF(!physicalId);
                 flinger->mutableHwcPhysicalDisplayIdMap().emplace(mHwcDisplayId, *physicalId);
                 if (mIsPrimary) {
-                    flinger->mutableInternalHwcDisplayId() = mHwcDisplayId;
+                    flinger->mutablePrimaryHwcDisplayId() = mHwcDisplayId;
                 } else {
-                    // If there is an external HWC display there should always be an internal ID
+                    // If there is an external HWC display, there should always be a primary ID
                     // as well. Set it to some arbitrary value.
-                    auto& internalId = flinger->mutableInternalHwcDisplayId();
-                    if (!internalId) internalId = mHwcDisplayId - 1;
-                    flinger->mutableExternalHwcDisplayId() = mHwcDisplayId;
+                    auto& primaryId = flinger->mutablePrimaryHwcDisplayId();
+                    if (!primaryId) primaryId = mHwcDisplayId - 1;
                 }
             }
         }