refactor: remove chrono as dependency (#4344)

Description
---
Remove dependency on chrono for birthday calculation in cipherseed

Motivation and Context
---
The wallet recovery uses a few extra days before the actual birthday when scanning, so being accurate to the timezone is not necessary, and certainly doesn't need an extra crate to calculate it.

How Has This Been Tested?
---
tests

base_layer/key_manager/Cargo.toml

@@ -19,7 +19,6 @@ arrayvec = "0.7.1"
 argon2 = { version = "0.2", features = ["std"] }
 blake2 = "0.9.1"
 chacha20 = "0.7.1"
-chrono = { version = "0.4.19", default-features = false, features = ["serde"] }
 clear_on_drop = "=0.2.4"
 console_error_panic_hook = "0.1.7"
 crc32fast = "1.2.1"

base_layer/key_manager/src/cipher_seed.rs

@@ -20,7 +20,11 @@
 // WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE
 // USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-use std::{convert::TryFrom, mem::size_of};
+use std::{
+    convert::TryFrom,
+    mem::size_of,
+    time::{SystemTime, UNIX_EPOCH},
+};
 
 use argon2::{password_hash::SaltString, Argon2, PasswordHasher};
 use arrayvec::ArrayVec;
@@ -34,6 +38,7 @@ use chacha20::{
 use crc32fast::Hasher as CrcHasher;
 use digest::Update;
 use rand::{rngs::OsRng, RngCore};
+use serde::{Deserialize, Serialize};
 use tari_utilities::ByteArray;
 
 use crate::{
@@ -82,7 +87,6 @@ pub const CIPHER_SEED_MAC_BYTES: usize = 5;
 /// The Birthday is included to enable more efficient recoveries. Knowing the birthday of the seed phrase means we
 /// only have to scan the blocks in the chain since that day for full recovery, rather than scanning the entire
 /// blockchain.
-use serde::{Deserialize, Serialize};
 
 #[derive(Clone, Debug, PartialEq, Eq, Serialize, Deserialize)]
 pub struct CipherSeed {
@@ -96,7 +100,7 @@ impl CipherSeed {
     #[cfg(not(target_arch = "wasm32"))]
     pub fn new() -> Self {
         const SECONDS_PER_DAY: u64 = 24 * 60 * 60;
-        let days = u64::try_from(chrono::Utc::now().timestamp()).unwrap() / SECONDS_PER_DAY;
+        let days = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs() / SECONDS_PER_DAY;
         let birthday = u16::try_from(days).unwrap_or(0u16);
         CipherSeed::new_with_birthday(birthday)
     }