After removing bootcamp partition, booting the mac it says insert bootable media and press any key? so I had to remove my bootcamp partition because I was running low on osx Sierra space and I didn't need the Windows partition. But when I boot the mac I get an error 


  No bootable device -- insert boot disk and press any key 


My guess is that there is still some sort of a Windows boot manager on a partition, but I can't see it in Diskutil GUI or when pressing Alt on startup, or in the startup disk. Currently, the only wat to boot to macOS is to hold down Alt then -> Macintosh HD,
Before selecting Macintosh HD in the Mac Startup Manager, hold down the control key. The straight arrow will become a circular arrow. This will make Sierra the default.

You can also make the Sierra the default, by selecting Macintosh HD from the Startup Disk pane of System Preferences.