In High-Sierra 10.13.6 on an Early 2011 Macbook Pro, I could clear-off the boot verbose mode nvram in normal boot mode itself. A reboot after that, booted without the logs.
RAJANANDPKsMBP:~ rajanandpk$ nvram boot-args
boot-args -v agc=0
RAJANANDPKsMBP:~ rajanandpk$ sudo nvram boot-args=""
Password:
RAJANANDPKsMBP:~ rajanandpk$ nvram boot-args
boot-args
RAJANANDPKsMBP:~ rajanandpk$ sudo nvram -d boot-args
RAJANANDPKsMBP:~ rajanandpk$ nvram boot-args
nvram: Error getting variable - 'boot-args': (iokit/common) data was not found