Remove inaccurate MIDI sequencer reference from heapq docs

Address review feedback: the parenthetical claimed a MIDI
sequencer exists in the standard library, which it does not.
Drop the reference and keep the sentence concise.

Author: bBlazewavE

Doc/library/heapq.rst

@@ -377,8 +377,7 @@ last 0'th element you extracted.  This is especially useful in simulation
 contexts, where the tree holds all incoming events, and the "win" condition
 means the smallest scheduled time.  When an event schedules other events for
 execution, they are scheduled into the future, so they can easily go into the
-heap.  So, a heap is a good structure for implementing schedulers (this is what
-was used for the MIDI sequencer in the standard library).
+heap.  So, a heap is a good structure for implementing schedulers.
 
 Various structures for implementing schedulers have been extensively studied,
 and heaps are good for this, as they are reasonably speedy, the speed is almost