travis: remove platform option arm64
travis: remove platform option arm64

[1] https://github.com/asciimoo/searx/pull/1910#issuecomment-607244871

Signed-off-by: Markus Heiser <14dfd67dd72e7ac80c040b62bb932f1e121795cc@darmarit.de>

dalf/searx,asciimoo/searx,dalf/searx,asciimoo/searx,asciimoo/searx,dalf/searx,asciimoo/searx,dalf/searx