Remove the former Dockerfile

Remove the former Dockerfile

opnfv/functest had been split into multiple containers based on
Alpine (See Docker Slicing [1]) during Euphrates.

As ARM is being switching to them, we can safely remove the related
files.

[1] https://git.opnfv.org/functest/tree/docs/com/pres/dockerslicing/dockerslicing.md?h=stable/euphrates

Conflicts:
    tox.ini
    setup.cfg

Change-Id: I30294a94cc742ba80a7bc4f35db9330240385bb0
Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
(cherry picked from commit 0705a7ed15f090b3be64f2995d1c9fff51edc2f1)