0030957: Assembly item Id should not start with '/' symbol

(cherry picked from commit 71b4fb4b10d050440971ca12af6d25e8989ec8ba)
(cherry picked from commit 7b296f0230)
(cherry picked from commit 93d0334ed84c0ea9163a55da791ab148bb14d0a4)

src/XCAFDoc/XCAFDoc_AssemblyItemId.cxx

@@ -119,5 +119,6 @@ XCAFDoc_AssemblyItemId::ToString() const
     aStr += '/';
     aStr += anIt.Value();
   }
+  aStr.Remove(1, 1);
   return aStr;
 }