Wallet: reduce excess logic InMemPool()

removed the excess logic, return directly instead of using if-statement.

src/wallet/wallet.cpp

@@ -1760,10 +1760,7 @@ CAmount CWalletTx::GetChange() const
 bool CWalletTx::InMempool() const
 {
     LOCK(mempool.cs);
-    if (mempool.exists(GetHash())) {
-        return true;
-    }
-    return false;
+    return mempool.exists(GetHash());
 }
 
 bool CWalletTx::IsTrusted() const