Remove now() fn workaround

[zrzka]

• chrono doesn't support wasm32 (see getting utc in wasm chronotope/chrono#243 & Add initial support for the wasm32 arch chronotope/chrono#287)
• we have added a workaround from the jjpe/wasm branch, which works, but ...

src/context.rs:

#[cfg(not(target_arch = "wasm32"))]
fn utc_now() -> DateTime<Utc> {
    Utc::now()
}

// chrono crate doesn't support wasm32 arch yet, workaround
#[cfg(target_arch = "wasm32")]
fn utc_now() -> DateTime<Utc> {
    let now = js_sys::Date::new_0();
    let millisecs_since_unix_epoch: u64 = now.get_time() as u64;
    let secs = millisecs_since_unix_epoch / 1000;
    let nanos = 1_000_000 * (millisecs_since_unix_epoch - 1000 * secs);
    let naive = NaiveDateTime::from_timestamp(secs as i64, nanos as u32);
    DateTime::from_utc(naive, Utc)
}