encoding/json: scanner: use byte, more consistent

The fields step and redoState of struct scanner are now defined as
`func(s *scanner, c byte) int` instead of
`func(s *scanner, c int) int`, since bytes are sufficient.
Further changes improve the consistency in the scanner.go file.

Change-Id: Ifb85f2130d728d2b936d79914d87a1f0b5c6ee7d
Reviewed-on: https://go-review.googlesource.com/14801
Reviewed-by: Andrew Gerrand <adg@golang.org>
Run-TryBot: Andrew Gerrand <adg@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/encoding/json/decode.go

@@ -241,7 +241,7 @@ func (d *decodeState) scanWhile(op int) int {
 			newOp = d.scan.eof()
 			d.off = len(d.data) + 1 // mark processed EOF with len+1
 		} else {
-			c := int(d.data[d.off])
+			c := d.data[d.off]
 			d.off++
 			newOp = d.scan.step(&d.scan, c)
 		}