zpool-features.5: remove "booting not possible with this feature"s

The exact limitations on what features are supported when booting
vary considerably depending on the environment.  In order to minimize
confusion avoid categorical statements which assume GRUB2 is being 
used.  The supported GRUB2 features are covered earlier in this man 
page for easy reference.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes openzfs#11842

man/man5/zpool-features.5

@@ -649,8 +649,6 @@ will be compressed with \fBlz4\fR algorithm. Since this feature is not
 read-only compatible, this operation will render the pool unimportable
 on systems without support for the \fBlz4_compress\fR feature.
 
-Booting off of \fBlz4\fR-compressed root pools is supported.
-
 This feature becomes \fBactive\fR as soon as it is enabled and will
 never return to being \fBenabled\fB.
 .RE
@@ -977,8 +975,6 @@ on \fBzstd\fR compression of any dataset by running
 This feature becomes \fBactive\fR once a \fBcompress\fR property has been set to
 \fBzstd\fR, and will return to being \fBenabled\fR once all filesystems that
 have ever had their compress property set to \fBzstd\fR are destroyed.
-
-Booting off of \fBzstd\fR-compressed root pools is not yet supported.
 .RE
 
 .SH "SEE ALSO"