dependabot: drop open-pull-requests-limit

There seems to be a bug in dependabot where sometimes it refuses to open
PRs due to hitting the pull request limit despite no PRs being open. The
rust-vmm/kvm repository ran into this. To avoid this in the future, drop
the open-pull-requests-limit key, which fixed the issue for
rust-vmm/kvm. In practice, due to us only having a single submodule and
due to cargo updates being grouped, we can only get at most one PR per
ecosystem at a time anyway.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

dependabot-monthly.yml

@@ -1,12 +1,15 @@
 version: 2
 updates:
 
+# We do not set open-pull-requests-limit, as sometimes
+# dependabot thinks the limit is hit without actually having
+# any PRs open. In reality, the configs below can only result
+# in at most one PR per package ecosyste manyway.
 # A monthly update of the rust-vmm-ci submodule
 - package-ecosystem: gitsubmodule
   directory: "/"
   schedule:
     interval: monthly
-  open-pull-requests-limit: 1
 
 # A monthly update to rust dependencies. These will be grouped,
 # e.g. one PR will contains updates for all dependencies.
@@ -14,7 +17,6 @@ updates:
   directory: "/"
   schedule:
     interval: monthly
-  open-pull-requests-limit: 1
   # Make it also update transitive dependencies in Cargo.lock
   allow:
     - dependency-type: "all"

dependabot-weekly.yml

@@ -1,13 +1,16 @@
 version: 2
 updates:
 
+# We do not set open-pull-requests-limit, as sometimes
+# dependabot thinks the limit is hit without actually having
+# any PRs open. In reality, the configs below can only result
+# in at most one PR per package ecosyste manyway.
 # A weekly update of the rust-vmm-ci submodule
 - package-ecosystem: gitsubmodule
   directory: "/"
   schedule:
     interval: weekly
     day: monday
-  open-pull-requests-limit: 1
 
 # A weekly update to rust dependencies. These will be grouped,
 # e.g. one PR will contains updates for all dependencies.
@@ -16,7 +19,6 @@ updates:
   schedule:
     interval: weekly
     day: monday
-  open-pull-requests-limit: 1
   # Make it also update transitive dependencies in Cargo.lock
   allow:
     - dependency-type: "all"