Revert "Reading environment var base64-encoded"

This reverts commit a0a8064d.
It is actually not necessary to use the base64 encoding anymore,
because the reason for which the variable was not passed to the
runner was the fact that the branch was not protected.

.gitlab-ci.yml

@@ -24,13 +24,7 @@ build:lektor:
     - mkdir -p ~/.ssh
     - chmod 700 ~/.ssh
     - eval $(ssh-agent -s)
-    #
-    # See https://gitlab.com/gitlab-org/gitlab-ce/issues/14434
-    # To avoid issues with the newlines and the encoding, the variable
-    # should contain the base64 encoding of the private key as follows:
-    # $ cat deploy_key | base64 -w0
-    #
-    - ssh-add <(echo "${DEPLOY_KEY}" | base64 -d)
+    - echo "${DEPLOY_KEY}" | tr -d '\r' | ssh-add - > /dev/null
     - ssh-keyscan -p ${DEPLOY_PORT} "${DEPLOY_HOST}" >> ~/.ssh/known_hosts
     - chmod 644 ~/.ssh/known_hosts
   only: