remove snapshots section

The JFrog account was deactivated so the links no longer work.

Fixes: ev3dev/ev3dev#1570

Author: dlech

docs/getting-started.md

@@ -291,4 +291,3 @@ favorite language is probably supported. Pick your language and write some code!
 [microSDHC]: https://en.wikipedia.org/wiki/Secure_Digital#SDHC
 [microSDXC]: https://en.wikipedia.org/wiki/Secure_Digital#SDXC
 [releases]:https://github.com/ev3dev/ev3dev/releases
-[nightly]:https://ev3dev.jfrog.io/artifactory/snapshots/

downloads.md

@@ -142,21 +142,6 @@ redirect_from: /download/
     <h1>Other Images</h1>
 </div>
 <div class="row">
-    <div class="col-md-6">
-        <h2>Snapshot Releases</h2>
-        <p>
-            We occasionally build images for testing purposes. These images
-            are published without any prior testing and there are no release
-            notes. However, you might be interested in these images if you
-            want to try out the latest new features and bug fixes.
-        </p>
-        <div class="margin-top-md">
-            <a class="btn btn-md btn-primary" href="https://ev3dev.jfrog.io/artifactory/snapshots/">
-                <span class="glyphicon glyphicon-link"></span>
-                Snapshots
-            </a>
-        </div>
-    </div>
     <div class="col-md-6">
         <h2>Previous Releases</h2>
         <p>