syscall work, rename syscall to sysvar, rename current to clock (#5074)

* syscall work, rename syscall to sysvar, rename current to clock

* missed one

* nit

sdk/src/lib.rs

@@ -17,10 +17,10 @@ pub mod pubkey;
 pub mod rpc_port;
 pub mod short_vec;
 pub mod signature;
-pub mod syscall;
 pub mod system_instruction;
 pub mod system_program;
 pub mod system_transaction;
+pub mod sysvar;
 pub mod timing;
 pub mod transaction;
 pub mod transport;