Cleanup VCMDecoderDataBase and neigbour VCMGenericDecoder classes

Remove private members that are no longer used or always have same value
Use less allocations

Bug: None
Change-Id: I5430c2356f0039212baf8b248b92775e8852ce1b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/227765
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34665}
diff --git a/modules/video_coding/generic_decoder_unittest.cc b/modules/video_coding/generic_decoder_unittest.cc
index a4cc5b0..6237c96 100644
--- a/modules/video_coding/generic_decoder_unittest.cc
+++ b/modules/video_coding/generic_decoder_unittest.cc
@@ -10,6 +10,7 @@
 
 #include "modules/video_coding/generic_decoder.h"
 
+#include <memory>
 #include <vector>
 
 #include "absl/types/optional.h"
@@ -68,7 +69,7 @@
         task_queue_factory_(CreateDefaultTaskQueueFactory()),
         decoder_(task_queue_factory_.get()),
         vcm_callback_(&timing_, &clock_),
-        generic_decoder_(&decoder_, /*isExternal=*/true) {}
+        generic_decoder_(&decoder_) {}
 
   void SetUp() override {
     generic_decoder_.RegisterDecodeCompleteCallback(&vcm_callback_);