SF: Remove HWC plumbing for virtual display mirror

Replace the parameter, which is only relevant to SF-ARC, with a simpler
hook (virtual processDisplayAdded) that is closer to HWC-less overrides
for display creation.

Bug: 182939859
Test: Build
Change-Id: I9c8f84ec900d6538d9130c23a75ee79d1aefe13e
diff --git a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
index caf0294..09734c2 100644
--- a/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
+++ b/services/surfaceflinger/DisplayHardware/ComposerHal.cpp
@@ -212,7 +212,7 @@
 }
 
 Error Composer::createVirtualDisplay(uint32_t width, uint32_t height, PixelFormat* format,
-                                     std::optional<Display>, Display* outDisplay) {
+                                     Display* outDisplay) {
     const uint32_t bufferSlotCount = 1;
     Error error = kDefaultError;
     if (mClient_2_2) {