go/parser: improved error message for unexpected literals
go/parser: improved error message for unexpected literals

R=go1.11

This is a follow up for #11377 which reported that an error like

/tmp/xx.go:9:6: expected '(', found 'IDENT' F1

shouldn't print 'IDENT', as it's just an internal detail.
The relevant change wasn't made in the original fix, so here it is.

For #11377.

Change-Id: Ib76957d86b88e3e63646fbe4abf03a3b9d045139
Reviewed-on: https://go-review.googlesource.com/87900
Reviewed-by: Matthew Dempsky <e56ac2c500064424afac424d4b5e53bd0570a731@google.com>

codestation/go,nawawi/go,josharian/go,akutz/go,Cofyc/go,golang/go,CAFxX/go,Cofyc/go,Cofyc/go,akutz/go,josharian/go,josharian/go,CAFxX/go,golang/go,codestation/go,nawawi/go,josharian/go,josharian/go,CAFxX/go,cloudflare/go,nawawi/go,codestation/go,codestation/go,codestation/go,akutz/go,Cofyc/go,CAFxX/go,CAFxX/go,akutz/go,golang/go,codestation/go,Cofyc/go,nawawi/go,golang/go,josharian/go,Cofyc/go,Cofyc/go,akutz/go,akutz/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,golang/go,codestation/go,cloudflare/go,nawawi/go,josharian/go,golang/go,cloudflare/go,josharian/go,akutz/go,cloudflare/go,nawawi/go,CAFxX/go,akutz/go,cloudflare/go,Cofyc/go,codestation/go,golang/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go