get rid of to_byte_slice and get_symbol_for

[b-ma]

• to_byte_slice can be avoided by doing e.g.:

let mut float32_arr_value = float32_arr.into_value()?;
let buffer: &mut [f32] = float32_arr_value.as_mut();
buffer.copy_from_slice(f32_slice);

• get_symbol_for is silly