Remove bitflags dependency for consistency

[MirkoCovizzi]

Removed because either we use bitflags everywhere or we don't. Since bitflags are macros, they add more friction when it comes to linting, I propose to remove this dependency and keep the more idiomatic way of using a C-like enum and casting to i32 or u32 as needed.

[m-hilgendorf]

That's a good point. It will also speed up compile times.