build: remove old version*.go files from hgignore

This broke a build on a Linux box I hadn't updated
in awhile. The hgignore files were preventing hg status
from showing and hg purge from cleaning up junk.

R=golang-dev, dsymonds
CC=golang-dev
https://golang.org/cl/5687048

.hgignore

@@ -46,8 +46,6 @@ src/pkg/go/build/syslist.go
 src/pkg/go/doc/headscan
 src/pkg/runtime/goc2c
 src/pkg/runtime/mkversion
-src/pkg/runtime/version.go
-src/pkg/runtime/version_*.go
 src/pkg/runtime/z*
 src/pkg/unicode/maketables
 src/pkg/*.*/