Remove code to handle multiple with overflow for i32 and i64

[antoyo]

here because these types should always be native.

[smups]

Rust fully specifies integer overflow behaviour, unlike in C/C++.

From the rust book:

When you’re compiling in release mode with the --release flag, Rust does not include checks for integer overflow that cause panics. Instead, if overflow occurs, Rust performs two’s complement wrapping.

[antoyo]

Yes, but we specify here to wrap on overflow.