Remove 4.2.x branch from dependabot

Signed-off-by: Ryan Baxter <ryan.baxter@broadcom.com>

Author: ryanjbaxter

.github/dependabot.yml

@@ -1,26 +1,10 @@
 version: 2
 updates:
-  - package-ecosystem: "github-actions"
-    directory: "/"
-    target-branch: "4.2.x"
-    schedule:
-      interval: "weekly"
   - package-ecosystem: "github-actions"
     directory: "/"
     target-branch: "main"
     schedule:
       interval: "weekly"
-  - package-ecosystem: maven
-    directory: /
-    schedule:
-      interval: daily
-    target-branch: 4.2.x
-    ignore:
-      # only upgrade patch versions for maintenance branch
-      - dependency-name: "*"
-        update-types:
-          - version-update:semver-major
-          - version-update:semver-minor
   - package-ecosystem: maven
     directory: /
     schedule:
@@ -53,11 +37,6 @@ updates:
     directory: /docs
     schedule:
       interval: weekly
-  - package-ecosystem: npm
-    target-branch: 4.2.x
-    directory: /docs
-    schedule:
-      interval: weekly
   - package-ecosystem: npm
     target-branch: 4.3.x
     directory: /docs