Berrymix tag clean up

BUR #177 has been rejected.

create alias berrymixv3 -> berrymix
create alias berry_mix -> berrymix
nuke berrymixv2

• Berrymix variants should live under one tag
• Make naming consistent (colloquially it was never referred to with a space)
• Berrymix v2 does not exist (the only post tagged with it prior, post #13298, seemed to have been mistagged as the actual model used was DarkBerryMix, which seems to originate from here)

This bulk update request is pending automatic rejection in 5 days.

This bulk update request has been rejected because it was not approved within 45 days.

The bulk update request #177 (forum #1304) has been rejected by @DanbooruBot.

BUR #196 has been approved by @Lyren.

create alias berrymixv3 -> berrymix
create alias berry_mix -> berrymix
nuke berrymixv2

Round Dos

The bulk update request #196 (forum #1417) has been approved by @Lyren.