Code cleanup (#9992)

* Value assigned to a variable is never read before being overwritten

* The result of append is not used anywhere

* Suspicious assignment of range-loop vars detected

* Unused method receiver detected

* Revert "Auxiliary commit to revert individual files from 54edcb445484a2e5d79612e19af8e949b8861253"

This reverts commit bbd1e1beabf7b0c5cfc4f514dcc820062ad6c063.

* Method modifies receiver

* Fix test

* Duplicate imports detected

* Incorrectly formatted error string

* Types of function parameters can be combined

* One more "Unused method receiver detected"

* Unused parameter detected in function

time/slots/testing/mock.go

@@ -15,4 +15,4 @@ func (m *MockTicker) C() <-chan types.Slot {
 }
 
 // Done --
-func (m *MockTicker) Done() {}
+func (_ *MockTicker) Done() {}