Drop Evict extension point

The Evict extension point is not currently in use.
All DefaultEvictor plugin functionality is exposed through Filter and
PreEvictionFilter extension points instead.
Thus, no need to limit the number of evictors enabled.

pkg/api/types.go

@@ -73,7 +73,6 @@ type Plugins struct {
 	Sort              PluginSet
 	Deschedule        PluginSet
 	Balance           PluginSet
-	Evict             PluginSet
 	Filter            PluginSet
 	PreEvictionFilter PluginSet
 }