cmd/bootnode,internal/debug: fix some comments (#21623)

internal/debug/api.go

@@ -196,7 +196,7 @@ func (*HandlerT) Stacks() string {
 	return buf.String()
 }
 
-// FreeOSMemory returns unused memory to the OS.
+// FreeOSMemory forces a garbage collection.
 func (*HandlerT) FreeOSMemory() {
 	debug.FreeOSMemory()
 }