www/chromium: update to 91.0.4472.106

This is a bugfix release, see
https://chromium.googlesource.com/chromium/src/+log/91.0.4472.101..91.0.4472.106?pretty=fuller&n=10000

While here remove the hardcoded dependency on virtual_oss.

MFH: 2021Q2
(cherry picked from commit 8c17a97d68ab369d5be30d90d5720b260e520efd)