remove externals opencv and pycolorname since the are submodules now and have own repositories:

* https://gerrit.wikimedia.org/r/#/admin/projects/pywikibot/opencv
* https://gerrit.wikimedia.org/r/#/admin/projects/pywikibot/pycolorname

Change-Id: I2145e6dc61ba463bf6658edc83b4183c5eaa9e36