zfs-module-parameters.5: remove nonexistent parameters

zfs_arc_overflow_shift was never a parameter:
ca0bf58d65 ("Illumos 5497 - lock
contention on arcs_mtx") is the only result in
git log -Soverflow_shift, and it wasn't exposed then, nor is it now

zfs_read_chunk_size was renamed to zfs_vnops_read_chunk_size in
e53d678d4a ("Share zfs_fsync, zfs_read,
zfs_write, et al between Linux and FreeBSD")

zio_decompress_fail_fraction was never a parameter: it was added in
c3bd3fb4ac ("OpenZFS 9403 - assertion
failed in arc_buf_destroy()") as a developer aid for setting in zdb, but
it's a dangerous test tunable and has no place in public documentation,
(not to mention that it obviously doesn't work):
> Although this did uncover a few low priority issues, this
  unfortuantely also causes ztest to ASSERT in many locations where the
  code is working correctly since it is designed to fail on IO errors.
  Developers can manually set this variable with the '-o' option to find
  and debug issues.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Richard Laager <rlaager@wiktel.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12157

man/man5/zfs-module-parameters.5

@@ -2995,7 +2995,7 @@ Use \fB1\fR for yes and \fB0\fR for no (default).
 .sp
 .ne 2
 .na
-\fBzfs_read_chunk_size\fR (long)
+\fBzfs_vnops_read_chunk_size\fR (long)
 .ad
 .RS 12n
 Bytes to read per chunk
@@ -3998,19 +3998,6 @@ the zio pipeline is looping indefinitely.
 Default value: \fB0\fR.
 .RE
 
-.sp
-.ne 2
-.na
-\fBzio_decompress_fail_fraction\fR (int)
-.ad
-.RS 12n
-If non-zero, this value represents the denominator of the probability that zfs
-should induce a decompression failure. For instance, for a 5% decompression
-failure rate, this value should be set to 20.
-.sp
-Default value: \fB0\fR.
-.RE
-
 .sp
 .ne 2
 .na