This commit fixes #10416 by using an EPS-based file-format for embedding
images in the users guide, as opposed to a png. This is because 'latex'
in some distributions is actually 'pdflatex', which supports reading the
size of PNGs in DVI mode, while traditional latex does not.

Rather than fiddle with the build a whole bunch, it's easy and simple to
just convert the png into a eps file and embed that instead.

But apparently we already had an EPS file, added in
1cce2f51! But it was quite large, so
instead I used `convert` to shrink it down from 1.7MB to about 20kb, the
same size as the original PDF (by using level3 postscript, which is not
as wasteful.)

Signed-off-by: Austin Seipp <austin@well-typed.com>

Differential Revision: https://phabricator.haskell.org/D970

GHC Trac Issues: #10416

(cherry picked from commit ca39b96e)