tests: Reduce calls to InitS*Cache()

In src/test/fuzz/script_sigcache.cpp, we should really be setting up a
full working BasicTestingSetup. The initialize_ function is only run
once anyway.

In src/test/txvalidationcache_tests.cpp, the Dersig100Setup inherits
from BasicTestingSetup, which should have already set up a global script
execution cache without the need to explicitly call
InitScriptExecutionCache.

src/test/fuzz/script_sigcache.cpp

@@ -10,18 +10,21 @@
 #include <test/fuzz/FuzzedDataProvider.h>
 #include <test/fuzz/fuzz.h>
 #include <test/fuzz/util.h>
+#include <test/util/setup_common.h>
 
 #include <cstdint>
 #include <optional>
 #include <string>
 #include <vector>
 
+namespace {
+const BasicTestingSetup* g_setup;
+} // namespace
+
 void initialize_script_sigcache()
 {
-    static const ECCVerifyHandle ecc_verify_handle;
-    ECC_Start();
-    SelectParams(CBaseChainParams::REGTEST);
-    InitSignatureCache();
+    static const auto testing_setup = MakeNoLogFileContext<>();
+    g_setup = testing_setup.get();
 }
 
 FUZZ_TARGET_INIT(script_sigcache, initialize_script_sigcache)

src/test/txvalidationcache_tests.cpp

@@ -161,11 +161,6 @@ BOOST_FIXTURE_TEST_CASE(checkinputs_test, Dersig100Setup)
 {
     // Test that passing CheckInputScripts with one set of script flags doesn't imply
     // that we would pass again with a different set of flags.
-    {
-        LOCK(cs_main);
-        InitScriptExecutionCache();
-    }
-
     CScript p2pk_scriptPubKey = CScript() << ToByteVector(coinbaseKey.GetPubKey()) << OP_CHECKSIG;
     CScript p2sh_scriptPubKey = GetScriptForDestination(ScriptHash(p2pk_scriptPubKey));
     CScript p2pkh_scriptPubKey = GetScriptForDestination(PKHash(coinbaseKey.GetPubKey()));