Manual test suite: simplify thanks to release process changes.

Now we'll publish all upgrades on the test channel and will use this
for our QA. Only once our QA has passed, $WEBSITE_RELEASE_BRANCH
will be merged, which will advertise the upgrades on the stable channel (for
actual releases) and alpha releases (for anything else) as usual.

wiki/src/contribute/release_process/test.mdwn

@@ -233,16 +233,7 @@ tracked by tickets prefixed with `todo/test_suite:`.
 
   then:
 
-        # Set TAILS_CHANNEL accordingly:
-        
-        # For actual releases:
-        TAILS_CHANNEL=test
-        
-        # For other (~rc, ~alpha...) releases:
-        TAILS_CHANNEL=alpha
-        
-        # Run:
-        echo "TAILS_CHANNEL=\"${TAILS_CHANNEL}\"" | sudo tee --append /etc/os-release && \
+        echo "TAILS_CHANNEL=\"test\" | sudo tee --append /etc/os-release && \
         tails-upgrade-frontend-wrapper
 
   Else, use a local test setup: