Remove *.xml from gitignore
Remove *.xml from gitignore

With the move to RST-based documentation, there is no need to ignore XML files
in the source tree anymore.

Reviewed By: bgamari

Differential Revision: https://phabricator.haskell.org/D1554

sdiehl/ghc,nushio3/ghc,vikraman/ghc,snoyberg/ghc,olsner/ghc,gridaphobe/ghc,vTurbine/ghc,mettekou/ghc,snoyberg/ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,shlevy/ghc,nushio3/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,sgillespie/ghc,gridaphobe/ghc,vTurbine/ghc,ezyang/ghc,ezyang/ghc,tjakway/ghcjvm,vikraman/ghc,tjakway/ghcjvm,tjakway/ghcjvm,sgillespie/ghc,nushio3/ghc,nushio3/ghc,vTurbine/ghc,vikraman/ghc,snoyberg/ghc,vikraman/ghc,mettekou/ghc,ezyang/ghc,vTurbine/ghc,mcschroeder/ghc,gridaphobe/ghc,shlevy/ghc,sdiehl/ghc,sgillespie/ghc,snoyberg/ghc,mcschroeder/ghc,sdiehl/ghc,mcschroeder/ghc,GaloisInc/halvm-ghc,mettekou/ghc,olsner/ghc,nushio3/ghc,vTurbine/ghc,ezyang/ghc,GaloisInc/halvm-ghc,olsner/ghc,tjakway/ghcjvm,snoyberg/ghc,olsner/ghc,oldmanmike/ghc,oldmanmike/ghc,nushio3/ghc,gridaphobe/ghc,olsner/ghc,gridaphobe/ghc,sdiehl/ghc,vTurbine/ghc,olsner/ghc,sgillespie/ghc,mettekou/ghc,GaloisInc/halvm-ghc,vikraman/ghc,tjakway/ghcjvm,snoyberg/ghc,vikraman/ghc,sdiehl/ghc,GaloisInc/halvm-ghc,oldmanmike/ghc,sdiehl/ghc,tjakway/ghcjvm,vTurbine/ghc,snoyberg/ghc,gridaphobe/ghc,vikraman/ghc,ezyang/ghc,oldmanmike/ghc,GaloisInc/halvm-ghc,shlevy/ghc,mcschroeder/ghc,shlevy/ghc,ezyang/ghc,oldmanmike/ghc,mettekou/ghc,sgillespie/ghc,mettekou/ghc,ezyang/ghc,sgillespie/ghc,shlevy/ghc,oldmanmike/ghc,mcschroeder/ghc,mettekou/ghc,mcschroeder/ghc,oldmanmike/ghc,sgillespie/ghc,mcschroeder/ghc,tjakway/ghcjvm,gridaphobe/ghc,nushio3/ghc,olsner/ghc