go spec: clean up use of QualifiedIdent production.
go spec: clean up use of QualifiedIdent production.

Fixes issue 3763.

R=r, rsc, iant, ken
CC=golang-dev
http://codereview.appspot.com/6333066

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang