Removed const qualifier from c.snippets main function signature

The const qualifier, though accepted by most compilers, is not standard:
The C++98 standard says in section 3.6.1.2
> [The main function] shall have a return type of type int,
> but otherwise its type is implementation-defined.
> All implementations shall allow both the following definitions of main:
> > int main() and int main(int argc, char* argv[])