Disable Travis CI for macOS.
Disable Travis CI for macOS.

Travis's macOS VMs are too weak to complete the C++ build in an hour, and it's
routinely taking one or two hours for us to get a build host. (Travis stats
suggest they only have slots for 128 simultaneous builds globally.)

Microsoft/bond,chwarr/bond,tstein/bond,gencer/bond,Microsoft/bond,Microsoft/bond,tstein/bond,sapek/bond,sapek/bond,gencer/bond,sapek/bond,chwarr/bond,jdubrule/bond,chwarr/bond,chwarr/bond,sapek/bond,gencer/bond,Microsoft/bond,gencer/bond,Microsoft/bond,sapek/bond,jdubrule/bond,tstein/bond,jdubrule/bond,jdubrule/bond,tstein/bond,gencer/bond,tstein/bond,jdubrule/bond,sapek/bond,Microsoft/bond,jdubrule/bond,chwarr/bond,tstein/bond,chwarr/bond