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/stake/src/stake_instruction.rs

@@ -380,7 +380,7 @@ 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::rewards::check_id(&meta.pubkey) {
                     sysvar::rewards::create_account(1, 0.0, 0.0)
                 } else if sysvar::stake_history::check_id(&meta.pubkey) {
@@ -604,7 +604,7 @@ mod tests {
                     KeyedAccount::new(
                         &sysvar::clock::id(),
                         false,
-                        &mut sysvar::clock::create_account(1, 0, 0, 0, 0)
+                        &mut sysvar::clock::Clock::default().create_account(1)
                     ),
                     KeyedAccount::new(
                         &config::id(),