qgis: remove all grass references and dependencies (#3717)
qgis: remove all grass references and dependencies (#3717)

grass is (at least temporarily) being boneyarded. See the PR
 Homebrew/homebrew-core#676 for more details.
quantumsteve/homebrew-science,pditommaso/homebrew-science,heuermh/homebrew-science,dpo/homebrew-science,DabeDotCom/homebrew-science,andrewjpage/homebrew-science,parcollet/homebrew-science,kozo2/homebrew-science,maplesond/homebrew-science,philippbayer/homebrew-science