doc: remove a reference to a removed command
doc: remove a reference to a removed command

This fix the following warning:

    doc/source/news/1.0.x.txt:120: WARNING: unknown document: /reference/executables/grntest

kenhys/groonga,groonga/groonga,naoa/groonga,naoa/groonga,redfigure/groonga,redfigure/groonga,komainu8/groonga,hiroyuki-sato/groonga,kenhys/groonga,naoa/groonga,myokoym/groonga,kenhys/groonga,redfigure/groonga,groonga/groonga,hiroyuki-sato/groonga,groonga/groonga,myokoym/groonga,hiroyuki-sato/groonga,naoa/groonga,naoa/groonga,groonga/groonga,myokoym/groonga,naoa/groonga,cosmo0920/groonga,myokoym/groonga,groonga/groonga,komainu8/groonga,naoa/groonga,redfigure/groonga,kenhys/groonga,kenhys/groonga,kenhys/groonga,groonga/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,komainu8/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,redfigure/groonga,cosmo0920/groonga,komainu8/groonga,myokoym/groonga,komainu8/groonga,myokoym/groonga,cosmo0920/groonga,groonga/groonga,naoa/groonga,komainu8/groonga,redfigure/groonga,komainu8/groonga,groonga/groonga,hiroyuki-sato/groonga,redfigure/groonga,komainu8/groonga,hiroyuki-sato/groonga,kenhys/groonga,cosmo0920/groonga,myokoym/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,cosmo0920/groonga,myokoym/groonga,redfigure/groonga,kenhys/groonga