Revert the fixes for the "vulnerable command line parsing"

revert these commits:
- e615c8c63f
- 45c245645d.
- cc1192c7d9.

CPP/Common/MyString.cpp

@@ -1206,16 +1206,6 @@ UString &UString::operator=(const UString &s)
   return *this;
 }
 
-void UString::AddFrom(const wchar_t *s, unsigned len) // no check
-{
-  if (len) {
-    Grow(len);
-    wmemcpy(_chars + _len, s, len);
-    _len += len;
-    _chars[_len] = 0;
-  }
-}
-
 void UString::SetFrom(const wchar_t *s, unsigned len) // no check
 {
   if (len > _limit)