fix: drop deprecated install input

Upstream docker/setup-buildx-action@v3 warns that the install input is
deprecated; recommend BUILDX_BUILDER env var instead.

action.yml

@@ -10,10 +10,6 @@ inputs:
     description: 'BuildKit TCP endpoint. Defaults to the in-cluster service.'
     required: false
     default: 'tcp://buildkit.gitea.svc.cluster.local:1234'
-  install:
-    description: 'Set up docker build as alias to docker buildx build.'
-    required: false
-    default: 'false'
   version:
     description: 'buildx version to install (passed through).'
     required: false
@@ -26,5 +22,4 @@ runs:
       with:
         driver: remote
         endpoint: ${{ inputs.endpoint }}
-        install: ${{ inputs.install }}
         version: ${{ inputs.version }}