scripted-diff: rename CChainState -> Chainstate

-BEGIN VERIFY SCRIPT-
sed -i 's/CChainState/Chainstate/g' $(git grep -l CChainState ':(exclude)doc/release-notes*')
-END VERIFY SCRIPT-

Co-authored-by: MacroFake <falke.marco@gmail.com>

doc/developer-notes.md

@@ -962,7 +962,7 @@ void CTxMemPool::UpdateTransactionsFromBlock(...)
 
 ```C++
 // validation.h
-class CChainState
+class Chainstate
 {
 protected:
     ...
@@ -983,7 +983,7 @@ public:
 }
 
 // validation.cpp
-bool CChainState::PreciousBlock(BlockValidationState& state, CBlockIndex* pindex)
+bool Chainstate::PreciousBlock(BlockValidationState& state, CBlockIndex* pindex)
 {
     AssertLockNotHeld(m_chainstate_mutex);
     AssertLockNotHeld(::cs_main);