Rename and use the default ref instead of having a workflow_dispatch option

.github/workflows/update-lkg.yml

@@ -1,12 +1,7 @@
 name: Update LKG
 
 on:
-  workflow_dispatch:
-    inputs:
-      branchName:
-        description: "The name of the branch you'd like to update the Last Known Good (LKG) version of the compiler on."
-        required: true
-        default: "master"
+  workflow_dispatch: {}
 
 jobs:
   build:
@@ -14,8 +9,6 @@ jobs:
 
     steps:
     - uses: actions/checkout@v2
-      with:
-        ref: ${{ github.event.inputs.branchName }}
     - name: Use node version 12
       uses: actions/setup-node@v1
       with: