Refactor String8 to std::string calls

DisplayViewport::uniqueId is now std::string, so change the calls
appropriately. Do some additional cleanups and conversions.
This almost completely removes the dependency on String8.

Test: build only
Bug: 111108021
Change-Id: Ibbb6ca59e9061954d4a5fb930ef03d42cb0230db
diff --git a/core/jni/android_hardware_display_DisplayViewport.cpp b/core/jni/android_hardware_display_DisplayViewport.cpp
index 23c3877..ab8e685 100644
--- a/core/jni/android_hardware_display_DisplayViewport.cpp
+++ b/core/jni/android_hardware_display_DisplayViewport.cpp
@@ -61,7 +61,7 @@
     jstring uniqueId =
             jstring(env->GetObjectField(viewportObj, gDisplayViewportClassInfo.uniqueId));
     if (uniqueId != nullptr) {
-        viewport->uniqueId.setTo(ScopedUtfChars(env, uniqueId).c_str());
+        viewport->uniqueId = ScopedUtfChars(env, uniqueId).c_str();
     }
 
     jobject logicalFrameObj =