all: switch out defunct set library to different one (#16873)

* keystore, ethash, eth, miner, rpc, whisperv6: tech debt with now defunct set.

* whisperv5: swap out gopkg.in/fatih/set.v0 with supported set

vendor/github.com/deckarep/golang-set/iterator.go

@@ -0,0 +1,58 @@
+/*
+Open Source Initiative OSI - The MIT License (MIT):Licensing
+
+The MIT License (MIT)
+Copyright (c) 2013 Ralph Caraveo (deckarep@gmail.com)
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+package mapset
+
+// Iterator defines an iterator over a Set, its C channel can be used to range over the Set's
+// elements.
+type Iterator struct {
+	C    <-chan interface{}
+	stop chan struct{}
+}
+
+// Stop stops the Iterator, no further elements will be received on C, C will be closed.
+func (i *Iterator) Stop() {
+	// Allows for Stop() to be called multiple times
+	// (close() panics when called on already closed channel)
+	defer func() {
+		recover()
+	}()
+
+	close(i.stop)
+
+	// Exhaust any remaining elements.
+	for range i.C {
+	}
+}
+
+// newIterator returns a new Iterator instance together with its item and stop channels.
+func newIterator() (*Iterator, chan<- interface{}, <-chan struct{}) {
+	itemChan := make(chan interface{})
+	stopChan := make(chan struct{})
+	return &Iterator{
+		C:    itemChan,
+		stop: stopChan,
+	}, itemChan, stopChan
+}