internal/jsonrpc2: remove unused invalidID constant

Change-Id: If00f4459be3176a44f7654bb304e03d9d6b393c2
Reviewed-on: https://go-review.googlesource.com/c/tools/+/288273
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
Trust: Rebecca Stambler <rstambler@golang.org>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

internal/jsonrpc2/wire.go

@@ -7,7 +7,6 @@ package jsonrpc2
 import (
 	"encoding/json"
 	"fmt"
-	"math"
 )
 
 // this file contains the go forms of the wire specification
@@ -122,8 +121,6 @@ func (wireVersionTag) UnmarshalJSON(data []byte) error {
 	return nil
 }
 
-const invalidID int64 = math.MaxInt64
-
 // NewIntID returns a new numerical request ID.
 func NewIntID(v int64) ID { return ID{number: v} }