remove appveyor (#5413)

AppVeyor has been more detrimental than actually helpful with regards to CI testing:

- Users are unable to re-build their own failing PRs. A project admin has to rebuild the PR
- The project somehow mixes up bacongobbler/helm with Helm/helm when observing CI status
- The only contributors able to test legitimate Windows failures lands on the shoulders of contributors with Windows devices

This removes Appveyor from Helm 3 testing until we can figure out a better solution.

Signed-off-by: Matthew Fisher <matt.fisher@microsoft.com>

.appveyor.yml

@@ -1,20 +0,0 @@
-version: "{build}"
-clone_folder: c:\go\src\k8s.io\helm
-environment:
-  GOPATH: c:\go
-  GOCACHE: c:\go\cache
-  PATH: c:\ProgramData\bin;$(PATH)
-install:
-  - ps: iex ((New-Object System.Net.WebClient).DownloadString('https://raw.githubusercontent.com/fishworks/gofish/master/scripts/install.ps1'))
-  - gofish init
-  - gofish install dep
-  - go version
-  - dep ensure -vendor-only -v
-cache:
-  - c:\go\pkg\dep -> Gopkg.lock
-  - c:\go\cache
-build: "off"
-deploy: "off"
-test_script:
-  - go build .\cmd\...
-  - go test .\...