Revert "require stake, vote and executable accounts to be rent exempt (#5928)" (#6005)

This reverts commit 11e6197a83.

sdk/src/sysvar/rent.rs

@@ -49,16 +49,6 @@ pub fn create_account(lamports: u64, rent_calculator: &RentCalculator) -> Accoun
     .unwrap()
 }
 
-use crate::account::KeyedAccount;
-use crate::instruction::InstructionError;
-
-pub fn from_keyed_account(account: &KeyedAccount) -> Result<Rent, InstructionError> {
-    if !check_id(account.unsigned_key()) {
-        return Err(InstructionError::InvalidArgument);
-    }
-    Rent::from_account(account.account).ok_or(InstructionError::InvalidArgument)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;