doc: Clarify waitTipChanged docs

It should be obvious that a wait is not needed if the tip does not
match.

Also, remove a comment that the blockTip notification was only meant for
the "UI". (It is used by other stuff for a long time)

src/interfaces/mining.h

@@ -64,8 +64,7 @@ public:
      * Waits for the tip to change
      *
      * @param[in] current_tip block hash of the current chain tip. Function waits
-     *                        for the chain tip to change if this matches, otherwise
-     *                        it returns right away.
+     *                        for the chain tip to differ from this.
      * @param[in] timeout     how long to wait for a new tip
      * @returns               Hash and height of the current chain tip after this call.
      */

src/validation.cpp

@@ -3533,7 +3533,6 @@ bool Chainstate::ActivateBestChain(BlockValidationState& state, std::shared_ptr<
                     m_chainman.m_options.signals->UpdatedBlockTip(pindexNewTip, pindexFork, still_in_ibd);
                 }
 
-                // Always notify the UI if a new block tip was connected
                 if (kernel::IsInterrupted(m_chainman.GetNotifications().blockTip(GetSynchronizationState(still_in_ibd, m_chainman.m_blockman.m_blockfiles_indexed), *pindexNewTip))) {
                     // Just breaking and returning success for now. This could
                     // be changed to bubble up the kernel::Interrupted value to