Add time since genesis to sysvar::clock (#7289)

* genesis timestamp

* remove clock::create_account()

* ..

* add configure-able creation time

* dividing by 1T, should be dividing by 1B

programs/vote/src/vote_instruction.rs

@@ -206,7 +206,7 @@ mod tests {
             .iter()
             .map(|meta| {
                 if sysvar::clock::check_id(&meta.pubkey) {
-                    sysvar::clock::create_account(1, 0, 0, 0, 0)
+                    sysvar::clock::Clock::default().create_account(1)
                 } else if sysvar::slot_hashes::check_id(&meta.pubkey) {
                     sysvar::slot_hashes::create_account(1, &[])
                 } else if sysvar::rent::check_id(&meta.pubkey) {