Clean up some outdated comments (#8418)

Authored-by: Gergely Risko <gergely@risko.hu>
Signed-off-by: Austin Seipp <austin@well-typed.com>
Release note fix.

Thanks to Gergely Risko for pointing this out.

Signed-off-by: Austin Seipp <austin@well-typed.com>
Turn -H and -Rghc-timing into dynamic flags.

Signed-off-by: Austin Seipp <austin@well-typed.com>