Call Must(En|De)code instead of (En|De)code to save time

Encode/Decode returns an error code, which we are generally not
checking for sub-objects because we never expect it to fail.  In the
new version of codegen Encode() sets up a panic handler and calls
MustEncode(), and the panic handler has a performance cost.  So just
call MustEncode() and if for some reason the encoding does fail we
will see it as a panic.

We still call Encode/Decode at top level and check the return code.

report/controls.go

@@ -91,7 +91,7 @@ type wireNodeControls struct {
 
 // CodecEncodeSelf implements codec.Selfer
 func (nc *NodeControls) CodecEncodeSelf(encoder *codec.Encoder) {
-	encoder.Encode(wireNodeControls{
+	encoder.MustEncode(wireNodeControls{
 		Timestamp: renderTime(nc.Timestamp),
 		Controls:  nc.Controls,
 	})