Remove unused headers from hsStlUtils.h (and push them downstream where needed)

Also fix a couple of plString and header issues identified by Paradox on GCC/Clang

Sources/Plasma/PubUtilLib/plAvatar/plAGAnim.h

@@ -50,8 +50,8 @@ You can contact Cyan Worlds, Inc. by email legal@cyan.com
 */
 #pragma warning(disable: 4786)      // don't care if mangled names are longer than 255 characters
 
+#include <map>
 #include "pnNetCommon/plSynchedObject.h"
-#include "hsStlUtils.h"
 #include "hsStlSortUtils.h"
 
 class plTMController;