How can I remove a pre-installed application on macOS Sierra
You technically can remove Safari by weakening your system's security protections and disabling SIP.

Again: Do not do it!

Steps:


Reboot on the recovery partition (hold cmd-R while rebooting until the Apple logo appears)
Open the Terminal from the Utilities menu
Type csrutil disable
Reboot
You should now able to remove Safari (if the Finder does not let you do it, use the Terminal and type sudo rm -fr /Applications/Safari.app)
I'd highly recommend you reactivate SIP then by rebooting and typing csrutil enable (it won't reinstall Safari)