validationcaches: Abolish arbitrary limit

1. -maxsigcachesize is a DEBUG_ONLY option

2. Almost 7 years has passed since its semantics change in
   830e3f3d027ba5c8121eed0f6a9ce99961352572 from "number of entries" to
   "number of mebibytes"

3. A std::new_handler was added to the codebase after the original PR
   which introduced this limit, which will terminate immediately instead
   of causing trouble by being caught somewhere unexpected.

src/script/sigcache.cpp

@@ -96,7 +96,7 @@ bool InitSignatureCache()
 {
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
-    size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+    size_t nMaxCacheSize = std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2) * ((size_t) 1 << 20);
 
     auto setup_results = signatureCache.setup_bytes(nMaxCacheSize);
 

src/script/sigcache.h

@@ -16,8 +16,6 @@
 // systems). Due to how we count cache size, actual memory usage is slightly
 // more (~32.25 MB)
 static const unsigned int DEFAULT_MAX_SIG_CACHE_SIZE = 32;
-// Maximum sig cache size allowed
-static const int64_t MAX_MAX_SIG_CACHE_SIZE = 16384;
 
 class CPubKey;
 

src/validation.cpp

@@ -1666,7 +1666,7 @@ bool InitScriptExecutionCache() {
     g_scriptExecutionCacheHasher.Write(nonce.begin(), 32);
     // nMaxCacheSize is unsigned. If -maxsigcachesize is set to zero,
     // setup_bytes creates the minimum possible cache (2 elements).
-    size_t nMaxCacheSize = std::min(std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2), MAX_MAX_SIG_CACHE_SIZE) * ((size_t) 1 << 20);
+    size_t nMaxCacheSize = std::max((int64_t)0, gArgs.GetIntArg("-maxsigcachesize", DEFAULT_MAX_SIG_CACHE_SIZE) / 2) * ((size_t) 1 << 20);
 
     auto setup_results = g_scriptExecutionCache.setup_bytes(nMaxCacheSize);