core: remove unnecessary assignment operator overloading

src/core/strings/dynamic_string.h

@@ -27,7 +27,6 @@ struct DynamicString
 
 	DynamicString(Allocator& a);
 
-	DynamicString& operator=(const DynamicString& ds);
 	DynamicString& operator=(const char* str);
 	DynamicString& operator=(const char c);
 	DynamicString& operator=(const FixedString& fs);
@@ -115,12 +114,6 @@ inline DynamicString& operator+=(DynamicString& a, const FixedString& fs)
 	return a;
 }
 
-inline DynamicString& DynamicString::operator=(const DynamicString& ds)
-{
-	_data = ds._data;
-	return *this;
-}
-
 inline DynamicString& DynamicString::operator=(const char* str)
 {
 	CE_ENSURE(NULL != str);