Had the same issue when I needed to use a tool that only worked with SNMPv2. I added the SNMP-SERVER COMMUNITY PUBLIC command, ran my tool, got what I needed, then went and tried to remove the PUBLIC community:
MyHost#no snmp-server community public
Community 'public' can't be deleted, as it is linked with another configuration.
I then remember seeing the word "public" somewhere, found it in "context" (as you showed in yours under SNMPv3). So I then thought to do the following:
MyHost# sh snmpv3 context
--------------------------------------------------------------------------
Name vrf Community
--------------------------------------------------------------------------
SNMPV3-Context default public
MyHost# config t
MyHost(config)# no snmpv3 context SNMPV3-Context vrf default
MyHost(config)# no snmp-server community public
MyHost(config)# snmpv3 context SNMPV3-Context vrf default
MyHost(config)# end
PUBLIC Community removed. All back to normal.