Remove DBG GcInfo encoder/decoder (dotnet#6374)

This change removes the redundant set of GcInfo encoder/decoder
in the CoreCLR tree called Debug encoder/decoders.

These components are expected to be are well-tested versions
for verification, but are not actively used.
They cause additional overhead wrt maintaining two versions of
GcInfo encoder/decoder as GcInfo format changes.

src/gcdump/gcdumpnonx86.cpp

@@ -522,6 +522,3 @@ void    GCDump::DumpPtrsInFrame(PTR_CBYTE   infoBlock,
 #define VALIDATE_ROOT(isInterior, hCallBack, pObjRef) ((void)0)
 #include "../vm/gcinfodecoder.cpp"
 #include "../gcinfo/gcinfodumper.cpp"
-#ifdef VERIFY_GCINFO
-#include "../vm/dbggcinfodecoder.cpp"
-#endif

src/gcinfo/CMakeLists.txt

@@ -3,7 +3,6 @@ set(CMAKE_INCLUDE_CURRENT_DIR ON)
 set( GCINFO_SOURCES
   arraylist.cpp
   gcinfoencoder.cpp
-  dbggcinfoencoder.cpp
 )
 
 if(CLR_CMAKE_PLATFORM_ARCH_I386)