drone.yml: using hte new drone gomobile image we can cut all the needless instructions

.drone.yml

@@ -58,18 +58,7 @@ steps:
       branch: trunk
       event: [ push, pull_request ]
     commands:
-        #- rm -rf /gomogile/pkg*
-        #- rm -rf /go/pkg
-        #- rm -rf /tmp/gomobile*
-        #- rm -rf vendor
-        #- go clean --modcache
-        #- export GOPATH=/gomobile
       - go mod download
-        #- go get golang.org/x/mobile/cmd/gomobile
-        #- go get golang.org/x/mobile/cmd/gobind
-      #- go get -u golang.org/x/mobile
-      #- go get -u golang.org/x/mobile/bind
-        # - gomobile clean
       - gomobile init
       - make android