snap: disable job until we are approved

We are waiting for snapcraft.io to review/approve us for "classic" mode.
reverts 1f684cf80a
ref #11482

.travis.yml

@@ -158,7 +158,7 @@ jobs:
       env:
         - CLANG_SANITIZER=TSAN
         - *common-job-env
-    - if: type != pull_request
+    - if: false
       name: snap
       os: linux
       env:

snap/snapcraft.yaml

@@ -12,7 +12,7 @@ description: |
  For lots more details, see the wiki!
 
 grade: stable  # must be 'stable' to release into candidate/stable channels
-confinement: devmode
+confinement: classic
 
 apps:
     nvim: