We no longer need to manually install faraday 1.8.0 as a work-around (#15976)

Faraday 2.0.1 re-introduces the default adapter (net_http), which
makes the prior work around (installing faraday 1.8 prior to
installing dpl, preventing it from bringing in 2.0.0 as the current
release).

There's currently a related dependency issue where a circular
dependency between dpl, faraday, and faraday-patron was causing deploy
failures (faraday-patron requiring faraday 2.0.x but we had
specified otherwise).

Remove the temporary shim to enable travis heroku deploys, and let
their team manage that.

.travis.yml

@@ -131,8 +131,7 @@ jobs:
     - stage: Deploy
       name: Deploy DEV
       if: type != pull_request
-      install:
-        -  rvm $(travis_internal_ruby) --fuzzy do ruby -S gem install faraday:"<2.0" dpl
+      install: skip
       script: skip
       after_script: skip
       deploy:
@@ -145,8 +144,7 @@ jobs:
     - stage: Deploy
       name: Deploy BenHalpern
       if: type != pull_request
-      install:
-        -  rvm $(travis_internal_ruby) --fuzzy do ruby -S gem install faraday:"<2.0" dpl
+      install: skip
       script: skip
       after_script: skip
       deploy: