Revert "docs: building Grafana on arm."

Further work-arounds are needed to make this work.
This reverts commit 8a2de587.

docs/sources/project/building_from_source.md

@@ -50,10 +50,6 @@ The Grafana backend includes Sqlite3 which requires GCC to compile. So in order
 npm --add-python-to-path='true' --debug install --global windows-build-tools
 ```
 
-#### Building on arm
-
-There is no `phantomjs-prebuilt` for arm, unfortunately that means that the frontend build will fail on arm. To fix this on arm, remove the `phantomjs-prebuilt` dependency (the whole line) from `package.json`. This also means that you won't be able to generate images of your graphs when running Grafana on arm.  
-
 ## Build the Frontend Assets
 
 For this you need nodejs (v.6+).