Simplify address checks in receiveApproval function (#405)

We can check directly msg.sender agains stbtc address and skip checking
the token address, as it is expected that the function will be called
only by the stBTC contract, and the token argument is not used anywhere,
besides the validation.

solidity/contracts/BitcoinRedeemer.sol

@@ -46,9 +46,6 @@ contract BitcoinRedeemer is Ownable2StepUpgradeable, IReceiveApproval {
     /// Reverts if the TBTCVault address is zero.
     error TbtcVaultZeroAddress();
 
-    /// Attempted to call receiveApproval for not supported token.
-    error UnsupportedToken(address token);
-
     /// Attempted to call receiveApproval by supported token.
     error CallerNotAllowed(address caller);
 
@@ -96,18 +93,16 @@ contract BitcoinRedeemer is Ownable2StepUpgradeable, IReceiveApproval {
     /// @notice Redeems shares for tBTC and requests bridging to Bitcoin.
     /// @param from Shares token holder executing redemption.
     /// @param amount Amount of shares to redeem.
-    /// @param token stBTC token address.
     /// @param extraData Redemption data in a format expected from
     ///        `redemptionData` parameter of Bridge's `receiveBalanceApproval`
     ///        function.
     function receiveApproval(
         address from,
         uint256 amount,
-        address token,
+        address,
         bytes calldata extraData
     ) external {
-        if (token != address(stbtc)) revert UnsupportedToken(token);
-        if (msg.sender != token) revert CallerNotAllowed(msg.sender);
+        if (msg.sender != address(stbtc)) revert CallerNotAllowed(msg.sender);
         if (extraData.length == 0) revert EmptyExtraData();
 
         redeemSharesAndUnmint(from, amount, extraData);

solidity/test/BitcoinDepositor.test.ts

@@ -748,7 +748,7 @@ describe("BitcoinDepositor", () => {
     extraDataValidTestData.forEach(
       (
         {
-          depositOwner: expoectedDepositOwner,
+          depositOwner: expectedDepositOwner,
           referral: expectedReferral,
           extraData,
         },
@@ -759,7 +759,7 @@ describe("BitcoinDepositor", () => {
             await bitcoinDepositor.decodeExtraData(extraData)
 
           expect(actualDepositOwner, "invalid depositOwner").to.be.equal(
-            expoectedDepositOwner,
+            expectedDepositOwner,
           )
           expect(actualReferral, "invalid referral").to.be.equal(
             expectedReferral,

solidity/test/BitcoinRedeemer.test.ts

@@ -63,7 +63,7 @@ describe("BitcoinRedeemer", () => {
               depositor.address,
               encodeBytes32String(""),
             ),
-        ).to.be.revertedWithCustomError(bitcoinRedeemer, "UnsupportedToken")
+        ).to.be.revertedWithCustomError(bitcoinRedeemer, "CallerNotAllowed")
       })
     })