This reverts commit 4f1a1bbce5. This was
intended to improve the development speed, but it breaks the build. This
is because even when cross-compiling, the Rust compiler does compile
some code for the host target for code-generation.
With the update to diesel 2.0.0-rc0, it is now possible to cross-compile
without emulation. Note that during each (cross)compile, we have to
install libpq-dev for the target platform, as only one version can be
installed at a time (e.g. libpq-dev:amd64 conflicts with libpq-dev:armhf).
