wallet: Remove unnecessary database Close step on shutdown

StopWallets, which was being called prior to UnloadWallets, performs an
unnecessary database closing step. This causes issues in UnloadWallets
which does additional database cleanups. Since the database closing step
is unnecessary, StopWallets is removed, and UnloadWallets is now called
from WalletLoaderImpl::stop.

src/wallet/interfaces.cpp

@@ -553,7 +553,7 @@ public:
         m_context.chain = &chain;
         m_context.args = &args;
     }
-    ~WalletLoaderImpl() override { UnloadWallets(m_context); }
+    ~WalletLoaderImpl() override { stop(); }
 
     //! ChainClient methods
     void registerRpcs() override
@@ -574,7 +574,7 @@ public:
         m_context.scheduler = &scheduler;
         return StartWallets(m_context);
     }
-    void stop() override { return StopWallets(m_context); }
+    void stop() override { return UnloadWallets(m_context); }
     void setMockTime(int64_t time) override { return SetMockTime(time); }
     void schedulerMockForward(std::chrono::seconds delta) override { Assert(m_context.scheduler)->MockForward(delta); }