Remove the "mypyc" benchmark

The original intent was that we would try to ensure that we ran
the mypy benchmark with the "mypy-built-with-mypyc" build of mypy.

Something got lost at some point and this needs a little bit of work
to make sure that pyperf installs an appropriate build (such as what
run_mypy.sh does), but for now it's still an improvement to get rid
of the "mypyc" benchmark.

Fixes #5

benchmarks/MANIFEST

@@ -9,7 +9,6 @@ gunicorn	<local>
 json	<local>
 kinto	<local>
 mypy	<local>
-mypyc	<local:mypy>
 pycparser	<local>
 pylint	<local>
 pytorch_alexnet_inference	<local>