fix: governance should not lock mempool mutex even call GetTransaction (#5175)

## Issue being fixed or feature implemented
Previously noticed, that GetTransaction is called deep inside governance
objects and it is true indeed.
But so far it is used `nullptr` as a mempol object instead any real
mempool in GetTransaction and no usage of a global mempool or any other
mempool, this locks are useless.

This changes are important for mempool globalization.

## What was done?
Removed LOCK for ::mempool.cs in governance's code

## How Has This Been Tested?
Run unit/functional tests. Also done deglobalization of mempool to
validate that governance indeed doesn't use global mempool implicit in
#5169

## Breaking Changes
No breaking changes

## Checklist:
- [x] I have performed a self-review of my own code
- [x] I have assigned this pull request to a milestone

Author: knst

src/governance/governance.cpp

@@ -142,8 +142,7 @@ void CGovernanceManager::ProcessMessage(CNode& peer, std::string_view msg_type,
             return;
         }
 
-        LOCK2(cs_main, ::mempool.cs); // Lock mempool because of GetTransaction deep inside
-        LOCK(cs);
+        LOCK2(cs_main, cs);
 
         if (mapObjects.count(nHash) || mapPostponedObjects.count(nHash) || mapErasedGovernanceObjects.count(nHash)) {
             // TODO - print error code? what if it's GOVOBJ_ERROR_IMMATURE?
@@ -262,8 +261,7 @@ void CGovernanceManager::AddGovernanceObject(CGovernanceObject& govobj, CConnman
 
     govobj.UpdateSentinelVariables(); //this sets local vars in object
 
-    LOCK2(cs_main, ::mempool.cs); // Lock mempool because of GetTransaction deep inside
-    LOCK(cs);
+    LOCK2(cs_main, cs);
     std::string strError;
 
     // MAKE SURE THIS OBJECT IS OK
@@ -320,8 +318,7 @@ void CGovernanceManager::UpdateCachesAndClean()
 
     std::vector<uint256> vecDirtyHashes = mmetaman.GetAndClearDirtyGovernanceObjectHashes();
 
-    LOCK2(cs_main, ::mempool.cs); // Lock mempool because of GetTransaction deep inside
-    LOCK(cs);
+    LOCK2(cs_main, cs);
 
     for (const uint256& nHash : vecDirtyHashes) {
         auto it = mapObjects.find(nHash);
@@ -835,8 +832,7 @@ void CGovernanceManager::CheckPostponedObjects(CConnman& connman)
 {
     if (!::masternodeSync->IsSynced()) return;
 
-    LOCK2(cs_main, ::mempool.cs); // Lock mempool because of GetTransaction deep inside
-    LOCK(cs);
+    LOCK2(cs_main, cs);
 
     // Check postponed proposals
     for (auto it = mapPostponedObjects.begin(); it != mapPostponedObjects.end();) {

src/governance/object.cpp

@@ -531,7 +531,6 @@ CAmount CGovernanceObject::GetMinCollateralFee(bool fork_active) const
 bool CGovernanceObject::IsCollateralValid(std::string& strError, bool& fMissingConfirmations) const
 {
     AssertLockHeld(cs_main);
-    AssertLockHeld(::mempool.cs); // because of GetTransaction
 
     strError = "";
     fMissingConfirmations = false;