crypto/tls,regexp: remove always-nil error results

These were harmless, but added unnecessary verbosity to the code.
This can happen as a result of refactors: for example,
the method sessionState used to return errors in some cases.

Change-Id: I4e6dacc01ae6a49b528c672979f95cbb86795a85
Reviewed-on: https://go-review.googlesource.com/c/go/+/528995
Reviewed-by: Leo Isla <islaleo93@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Olivier Mengué <olivier.mengue@gmail.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: qiulaidongfeng <2645477756@qq.com>
Reviewed-by: Quim Muntal <quimmuntal@gmail.com>

handshake_client.go

@@ -909,10 +909,7 @@ func (hs *clientHandshakeState) saveSessionTicket() error {
 		return nil
 	}
 
-	session, err := c.sessionState()
-	if err != nil {
-		return err
-	}
+	session := c.sessionState()
 	session.secret = hs.masterSecret
 
 	cs := &ClientSessionState{ticket: hs.ticket, session: session}