Fix dependabot | chore(ci) (#620)

Dependabot doesn't seem to pick up ort-nightly builds. Reverting to
check pip for now.

Author: justinchuby

.github/dependabot.yaml

@@ -4,20 +4,9 @@
 # https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
 
 version: 2
-registries:
-  pypi:
-    type: python-index
-    url: https://pypi.org/simple
-  ort-nightly-index:
-    type: python-index
-    url: https://aiinfra.pkgs.visualstudio.com/PublicPackages/_packaging/ORT-Nightly/pypi/simple/
-    replaces-base: true
 updates:
   - package-ecosystem: "pip" # See documentation for possible values
     directory: "/requirements/ci/" # Location of package manifests
-    registries:
-      - ort-nightly-index
-      - pypi
     schedule:
       interval: "daily"
     # disable version updates for pip dependencies