etc: Remove comments about nogroups and noroot on nvidia

`nogroups` should not have been causing issues with rendering on nvidia
since commit 623e682 ("temporary fix for nvidia/nogroups/noroot issue
(netblue30#3644, netblue30#841)", 2020-10-02) and commit cb460c3 ("more nvidia (netblue30#3644)",
2020-10-03), which had made it a no-op on nvidia.  And the handling of
the "render" and "video" groups are independent to the handling of
`nogroups` now; see the previous 3 commits.

Commits which introduced the comments on each profile:

* kodi.profile: commit ce462b6 ("fix netblue30#3501", 2020-07-16)
* mpsyt.profile: commit e17b48f ("new profile mpsyt.profile",
  2018-11-28)
* mpv.profile: commit cc7c489 ("Document netblue30#1945", 2018-07-25)
* steam.profile: commit d6f8169 ("steam fixes; netblue30#841, netblue30#3267",
  2020-03-15)

Commands used to find the comments:

    git grep -i nvidia -- etc/profile-* | grep -v private-etc

Relates to netblue30#4632.

etc/profile-a-l/kodi.profile

@@ -43,7 +43,6 @@ netfilter
 nogroups
 noinput
 nonewprivs
-# Seems to cause issues with Nvidia drivers sometimes (#3501)
 noroot
 nou2f
 protocol unix,inet,inet6,netlink

etc/profile-m-z/mpsyt.profile

@@ -50,7 +50,6 @@ apparmor
 caps.drop all
 netfilter
 nodvd
-# Seems to cause issues with Nvidia drivers sometimes
 nogroups
 noinput
 nonewprivs

etc/profile-m-z/mpv.profile

@@ -62,7 +62,6 @@ include whitelist-var-common.inc
 apparmor
 caps.drop all
 netfilter
-# nogroups seems to cause issues with Nvidia drivers sometimes
 nogroups
 noinput
 nonewprivs

etc/profile-m-z/steam.profile

@@ -132,7 +132,6 @@ netfilter
 nodvd
 nogroups
 nonewprivs
-# If you use nVidia you might need to add 'ignore noroot' to your steam.local.
 noroot
 notv
 nou2f