Remove Travis-CI configuration (#7674)
Remove Travis-CI configuration (#7674)

We've moved to Github CI exclusively, because Travis has unfortunately
become exceedingly slow.  Remove the obsolete configuration file.
esp8266/Arduino,sticilface/Arduino,sticilface/Arduino,esp8266/Arduino,sticilface/Arduino,sticilface/Arduino,esp8266/Arduino,esp8266/Arduino,sticilface/Arduino,esp8266/Arduino