remove workarounds for resolved issue 13049 and 13050

- [Issue 13049 – in template arguments the compiler fails to parse scope for function pointers arguments](https://issues.dlang.org/show_bug.cgi?id=13049)
- [Issue 13050 – pragma mangle breaks homonym template aliasing](https://issues.dlang.org/show_bug.cgi?id=13050)