DRTVWR-476: Eliminate unnecessary typedefs from struct, enum decls.

With VS 2017, these produced fatal warnings.

indra/llcommon/StackWalker.cpp

@@ -422,7 +422,7 @@ class StackWalkerInternal
   LPSTR m_szSymPath;
 
 #pragma pack(push,8)
-typedef struct IMAGEHLP_MODULE64_V3 {
+struct IMAGEHLP_MODULE64_V3 {
     DWORD    SizeOfStruct;           // set to sizeof(IMAGEHLP_MODULE64)
     DWORD64  BaseOfImage;            // base load address of module
     DWORD    ImageSize;              // virtual size of the loaded module
@@ -450,7 +450,7 @@ typedef struct IMAGEHLP_MODULE64_V3 {
     BOOL     Publics;                // contains public symbols
 };
 
-typedef struct IMAGEHLP_MODULE64_V2 {
+struct IMAGEHLP_MODULE64_V2 {
     DWORD    SizeOfStruct;           // set to sizeof(IMAGEHLP_MODULE64)
     DWORD64  BaseOfImage;            // base load address of module
     DWORD    ImageSize;              // virtual size of the loaded module

indra/llcommon/StackWalker.h

@@ -148,7 +148,7 @@ class StackWalker
     CHAR loadedImageName[STACKWALK_MAX_NAMELEN];
   } CallstackEntry;
 
-  typedef enum CallstackEntryType {firstEntry, nextEntry, lastEntry};
+  enum CallstackEntryType {firstEntry, nextEntry, lastEntry};
 
   virtual void OnSymInit(LPCSTR szSearchPath, DWORD symOptions, LPCSTR szUserName);
   virtual void OnLoadModule(LPCSTR img, LPCSTR mod, DWORD64 baseAddr, DWORD size, DWORD result, LPCSTR symType, LPCSTR pdbName, ULONGLONG fileVersion);