[net] Remove unnecessary cs_sendProcessing lock annotation

m_next_addr_send and m_next_local_addr_send do not need to be guarded by
cs_sendProcessing. These fields are only read/writen by the message
handling thread and the annotation was added unnecessarily in commit
b312cd7. See discussion at
bitcoin#13123 (comment).

Therefore remove this unnecessary lock annotation.

src/net.h

@@ -546,8 +546,8 @@ class CNode
     std::vector<CAddress> vAddrToSend;
     std::unique_ptr<CRollingBloomFilter> m_addr_known{nullptr};
     bool fGetAddr{false};
-    std::chrono::microseconds m_next_addr_send GUARDED_BY(cs_sendProcessing){0};
-    std::chrono::microseconds m_next_local_addr_send GUARDED_BY(cs_sendProcessing){0};
+    std::chrono::microseconds m_next_addr_send{0};
+    std::chrono::microseconds m_next_local_addr_send{0};
 
     struct TxRelay {
         mutable RecursiveMutex cs_filter;