Summary:
We can use `//` exclusively because we always build Eden with Buck and never
fbbuild, our legacy build system for fbcode.
This revision was initially created by running:
```
find eden -name TARGETS | xargs sed -i -e 's#@/#//#g'
```
And then manually updating the `DEFS` file now that we no longer need
some normalization code for an outdated pattern.
But then I got annoyed by other inconsistencies, so I went through and
alpha-sorted some lists, replaced all double quotes with single quotes,
and fixed indents to be two spaces.
Reviewed By: simpkins
Differential Revision: D4356724
fbshipit-source-id: ab07a48f12fa937c257213d12331efdf09e42da6
3f2f22d8fa