go/ast: remove many blank lines in SortImports
go/ast: remove many blank lines in SortImports

Currently only one blank line is checked to be removed.
Changing sort.Sort may lead to more blank lines.
Let's remove them all.

It fixes a bug found by https://golang.org/cl/15688

Change-Id: I682cc23ecd7b10d9b6feb160da040a155297f578
Reviewed-on: https://go-review.googlesource.com/17440
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

deft-code/go,vsekhar/elastic-go,theif519/go,Samurais/go,Endika/go,golang/go,linux-on-ibm-z/go,mwhudson/go,goodlang/good,odeke-em/go,nawawi/go,4ad/go,josharian/go,vanloswang/go,miolini/go,sndnvaps/go,ganboing/go-esx,Cofyc/go,Samurais/go,derekmarcotte/go,Samurais/go,derekmarcotte/go,nawawi/go,cyberroadie/go,ganboing/go-esx,cyberroadie/go,polyverse-security/go,polyverse-security/go,suncycheng/go,cyberroadie/go,fjballest/golang,Samurais/go,christopher-henderson/Go,cloudflare/go,miolini/go,nawawi/go,nawawi/go,miolini/go,akutz/go,roth1002/go,mwhudson/go,josharian/go,codestation/go,codestation/go,akutz/go,suncycheng/go,CAFxX/go,linux-on-ibm-z/go,roth1002/go,akutz/go,fjballest/golang,goodlang/good,ImJasonH/go,polyverse-security/go,cloudflare/go,cyberroadie/go,fjballest/golang,kim-racktop/go,Cofyc/go,odeke-em/go,linux-on-ibm-z/go,CAFxX/go,CAFxX/go,Endika/go,CAFxX/go,nawawi/go,miolini/go,Cofyc/go,josharian/go,mwhudson/go,CAFxX/go,momchil-velikov/go,vanloswang/go,derekmarcotte/go,suncycheng/go,deft-code/go,suncycheng/go,theif519/go,nawawi/go,CAFxX/go,4ad/go,codestation/go,josharian/go,sndnvaps/go,momchil-velikov/go,codestation/go,golang/go,nawawi/go,Endika/go,polyverse-security/go,deft-code/go,ImJasonH/go,nawawi/go,4ad/go,akutz/go,Samurais/go,odeke-em/go,polyverse-security/go,goodlang/good,vanloswang/go,theif519/go,codestation/go,odeke-em/go,odeke-em/go,kim-racktop/go,roth1002/go,sndnvaps/go,vsekhar/elastic-go,deft-code/go,josharian/go,cloudflare/go,mwhudson/go,miolini/go,theif519/go,deft-code/go,miolini/go,fjballest/golang,derekmarcotte/go,binarycrusader/go,goodlang/good,ImJasonH/go,vanloswang/go,golang/go,mwhudson/go,cloudflare/go,golang/go,golang/go,akutz/go,josharian/go,fjballest/golang,suncycheng/go,Cofyc/go,binarycrusader/go,mwhudson/go,binarycrusader/go,polyverse-security/go,derekmarcotte/go,akutz/go,roth1002/go,golang/go,Endika/go,momchil-velikov/go,mwhudson/go,binarycrusader/go,theif519/go,suncycheng/go,vsekhar/elastic-go,binarycrusader/go,suncycheng/go,linux-on-ibm-z/go,fjballest/golang,sndnvaps/go,vanloswang/go,linux-on-ibm-z/go,akutz/go,ganboing/go-esx,vanloswang/go,theif519/go,ganboing/go-esx,roth1002/go,golang/go,ImJasonH/go,4ad/go,theif519/go,CAFxX/go,suncycheng/go,4ad/go,sndnvaps/go,momchil-velikov/go,ganboing/go-esx,ganboing/go-esx,cloudflare/go,codestation/go,vsekhar/elastic-go,sndnvaps/go,Endika/go,cloudflare/go,ImJasonH/go,mwhudson/go,ImJasonH/go,vanloswang/go,vsekhar/elastic-go,ImJasonH/go,deft-code/go,vsekhar/elastic-go,CAFxX/go,polyverse-security/go,4ad/go,kim-racktop/go,Endika/go,vsekhar/elastic-go,codestation/go,kim-racktop/go,deft-code/go,Endika/go,Samurais/go,goodlang/good,sndnvaps/go,vanloswang/go,ImJasonH/go,binarycrusader/go,roth1002/go,binarycrusader/go,derekmarcotte/go,fjballest/golang,odeke-em/go,goodlang/good,Samurais/go,cyberroadie/go,4ad/go,kim-racktop/go,vsekhar/elastic-go,linux-on-ibm-z/go,odeke-em/go,kim-racktop/go,miolini/go,roth1002/go,ganboing/go-esx,Cofyc/go,golang/go,Cofyc/go,momchil-velikov/go,cyberroadie/go,polyverse-security/go,sndnvaps/go,cyberroadie/go,odeke-em/go,miolini/go,Samurais/go,momchil-velikov/go,josharian/go,Cofyc/go,4ad/go,binarycrusader/go,kim-racktop/go,momchil-velikov/go,linux-on-ibm-z/go,goodlang/good,codestation/go,josharian/go,deft-code/go,cyberroadie/go,goodlang/good,Cofyc/go,linux-on-ibm-z/go,akutz/go,kim-racktop/go,roth1002/go,ganboing/go-esx,momchil-velikov/go,fjballest/golang,Endika/go,cloudflare/go,cloudflare/go,derekmarcotte/go,theif519/go,derekmarcotte/go