Merge #21553: fuzz: Misc refactor

fa4926cca6 fuzz: [refactor] Use IsValidFlagCombination in signature_checker fuzz target (MarcoFalke)
eeee8f5be1 fuzz: Removed unused try-catch in coins_view (MarcoFalke)
fa98f3f66e fuzz: [refactor] Use ConsumeScript in signature_checker fuzz target (MarcoFalke)

Pull request description:

  Some small refactors to remove unused and redundant fuzz code

ACKs for top commit:
  practicalswift:
    cr re-ACK fa4926cca6

Tree-SHA512: eb07a2140caad7b31495b76385fc7634cf5b6daa4947f430ebb127eb1375583dc11e541a0a42d0e5d93d430480b8a815b93974450fd5ed897528a2d47c752f86

src/test/util/script.cpp

@@ -0,0 +1,13 @@
+// Copyright (c) 2021 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <script/interpreter.h>
+#include <test/util/script.h>
+
+bool IsValidFlagCombination(unsigned flags)
+{
+    if (flags & SCRIPT_VERIFY_CLEANSTACK && ~flags & (SCRIPT_VERIFY_P2SH | SCRIPT_VERIFY_WITNESS)) return false;
+    if (flags & SCRIPT_VERIFY_WITNESS && ~flags & SCRIPT_VERIFY_P2SH) return false;
+    return true;
+}

src/test/util/script.h

@@ -18,4 +18,7 @@ static const CScript P2WSH_OP_TRUE{
            return hash;
        }())};
 
+/** Flags that are not forbidden by an assert in script validation */
+bool IsValidFlagCombination(unsigned flags);
+
 #endif // BITCOIN_TEST_UTIL_SCRIPT_H