audio/lv2: Remove CONFLICTS_INSTALL

lv2core expired and was deleted on 2016-11-30 in ports r427460

I only noted this after committing ports r499627, so remove it accordingly.

PR: 235103
Approved by: Michael Beer <beerml sigma6audio de> (maintainer)
MFH: 2019Q2 (MFH with: r499627)