unicode: update table using new generator in x/text

The changes in Unicode 11 exposes a bug in maketables.go.
We update the Unicode 10 tables using a new generator
to minimize the changes upgrading to Unicode 11.

This change switches over the generation from core to that in
x/text. To properly update the tables one needs to run the generate
in x/text anyway, so this makes that official.

The RangeTable generator in x/text also generates slightly compacter
tables.

Updates golang/go#27945

See CL 154443

Change-Id: I6c59e082d5b8cd9e9332a32d8971061228581d66
Reviewed-on: https://go-review.googlesource.com/c/go/+/169617
Run-TryBot: Marcel van Lohuizen <mpvl@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/unicode/letter.go

@@ -6,9 +6,6 @@
 // Unicode code points.
 package unicode
 
-// Tables are regenerated each time we update the Unicode version.
-//go:generate go run maketables.go -tables=all -output tables.go
-
 const (
 	MaxRune         = '\U0010FFFF' // Maximum valid Unicode code point.
 	ReplacementChar = '\uFFFD'     // Represents invalid code points.