Simplify some Option / Result / ? operator patterns (#8653)

* Simplify some Option / Result / ? operator patterns

When those match a combinator exactly.

Tool-aided by [comby-rust](https://github.com/huitseeker/comby-rust).

* adjust after review

* adjust post-review

substrate/frame/contracts/src/gas.rs

@@ -127,10 +127,7 @@ where
 		}
 
 		let amount = token.calculate_amount(metadata);
-		let new_value = match self.gas_left.checked_sub(amount) {
-			None => None,
-			Some(val) => Some(val),
-		};
+		let new_value = self.gas_left.checked_sub(amount);
 
 		// We always consume the gas even if there is not enough gas.
 		self.gas_left = new_value.unwrap_or_else(Zero::zero);

substrate/frame/contracts/src/migration.rs

@@ -26,16 +26,12 @@ pub fn migrate<T: Config>() -> Weight {
 		Some(version) if version == PalletVersion::new(3, 0, 0) => {
 			weight = weight.saturating_add(T::DbWeight::get().reads_writes(1, 1));
 			let _ = <CurrentSchedule<T>>::translate::<u32, _>(|version| {
-				if let Some(version) = version {
-					Some(Schedule {
+				version.map(|version| Schedule {
 						version: version.saturating_add(1),
 						// Default limits were not decreased. Therefore it is OK to overwrite
 						// the schedule with the new defaults.
 						.. Default::default()
 					})
-				} else {
-					None
-				}
 			});
 		}
 		_ => (),

substrate/frame/contracts/src/rent.rs

@@ -407,10 +407,7 @@ where
 		);
 
 		// Check what happened after enaction of the verdict.
-		let alive_contract_info = match new_contract_info.map_err(|_| IsTombstone)? {
-			None => return Err(IsTombstone),
-			Some(contract) => contract,
-		};
+		let alive_contract_info = new_contract_info.map_err(|_| IsTombstone)?.ok_or_else(|| IsTombstone)?;
 
 		// Compute how much would the fee per block be with the *updated* balance.
 		let total_balance = T::Currency::total_balance(account);