fix Issue 8366 - Overriding const member function in conjunction with mutable overload causes a strange error

We MUST kill attribute inference with const. To implement it correctly without breaking overriding and overloading features, re-scanning and arrangement of vtbl entries is needed in the end of Classdeclaration::semantic, it will decrease compile speed.
I think that is a big drawbacks than the benefit.
Merge pull request #1042 from 9rnsr/fix8366

Issue 8366 - Overriding const member function in conjunction with mutable overload causes a strange error