Revert "doc: update Kernel documentation build system"

Unfortunately we now see a number of now-fatal warnings about duplicate
labels.  It is often unclear how best to re-write the document in
question to not duplicate these otherwise logical headings.

This reverts commit 10a1df3cd4.

Signed-off-by: Tom Rini <trini@konsulko.com>

doc/sphinx/parallel-wrapper.sh

@@ -1,33 +0,0 @@
-#!/bin/sh
-# SPDX-License-Identifier: GPL-2.0+
-#
-# Figure out if we should follow a specific parallelism from the make
-# environment (as exported by scripts/jobserver-exec), or fall back to
-# the "auto" parallelism when "-jN" is not specified at the top-level
-# "make" invocation.
-
-sphinx="$1"
-shift || true
-
-parallel="$PARALLELISM"
-if [ -z "$parallel" ] ; then
-	# If no parallelism is specified at the top-level make, then
-	# fall back to the expected "-jauto" mode that the "htmldocs"
-	# target has had.
-	auto=$(perl -e 'open IN,"'"$sphinx"' --version 2>&1 |";
-			while (<IN>) {
-				if (m/([\d\.]+)/) {
-					print "auto" if ($1 >= "1.7")
-				}
-			}
-			close IN')
-	if [ -n "$auto" ] ; then
-		parallel="$auto"
-	fi
-fi
-# Only if some parallelism has been determined do we add the -jN option.
-if [ -n "$parallel" ] ; then
-	parallel="-j$parallel"
-fi
-
-exec "$sphinx" $parallel "$@"