x/ibc/light-clients: simplify max time comparison (cosmos#8089)

The prior code that tried to get the newest/larger time
between the too performed:
* 2 time.Time.UnixNano() retrievals: 2 multiplications, 2 additions
* 1 math.Max comparison
* 1 time.Unix(0, minTime) creation

but really this code could just use native operations on:
time.Time.After() simply.

This now becomes a single operation, single comparison for the same effect.

x/ibc/light-clients/07-tendermint/types/misbehaviour.go

@@ -2,7 +2,6 @@ package types
 
 import (
 	"bytes"
-	"math"
 	"time"
 
 	tmproto "github.com/tendermint/tendermint/proto/tendermint/types"
@@ -48,8 +47,11 @@ func (misbehaviour Misbehaviour) GetHeight() exported.Height {
 // maximum value from both headers to prevent producing an invalid header outside
 // of the misbehaviour age range.
 func (misbehaviour Misbehaviour) GetTime() time.Time {
-	minTime := int64(math.Max(float64(misbehaviour.Header1.GetTime().UnixNano()), float64(misbehaviour.Header2.GetTime().UnixNano())))
-	return time.Unix(0, minTime)
+	t1, t2 := misbehaviour.Header1.GetTime(), misbehaviour.Header2.GetTime()
+	if t1.After(t2) {
+		return t1
+	}
+	return t2
 }
 
 // ValidateBasic implements Misbehaviour interface