Replace obsolete PCRE packages

pcre3 was removed from recent debian-based releases (eg. Trixie[1]),
while RHEL10/CentOS Stream 10 no longer ships pcre in favor of pcre2.

Use the latest whereto library release (0.5.0) which uses pcre2
instead.

[1] https://lists.debian.org/debian-devel/2021/11/msg00176.html

Depends-on: https://review.opendev.org/c/openstack/requirements/+/97142
Change-Id: I3defc6a343f5a211b0e7185017085371631b3dee
Signed-off-by: Takashi Kajinami <kajinamit@oss.nttdata.com>

bindep.txt

@@ -5,5 +5,5 @@
 #                  in docs job - if usage is extended - needs removal from
 #                  there.
 
-libpcre3-dev [platform:dpkg doc]
-pcre-devel [platform:rpm doc]
+libpcre2-dev [platform:dpkg doc]
+pcre2-devel [platform:rpm doc]

doc/requirements.txt

@@ -1,12 +1,5 @@
-# The order of packages is significant, because pip processes them in the order
-# of appearance. Changing the order has an impact on the overall integration
-# process, which may cause wedges in the gate later.
-# Order matters to the pip dependency resolver, so sorting this file
-# changes how packages are installed.  New dependencies should be
-# added in alphabetical order, however, some dependencies may need to
-# be installed in a specific order.
 openstackdocstheme>=2.2.1 # Apache-2.0
 reno>=3.1.0 # Apache-2.0
 sphinx>=2.0.0,!=2.1.0 # BSD
 sphinxcontrib-svg2pdfconverter>=0.1.0 # BSD
-whereto>=0.3.0 # Apache-2.0
+whereto>=0.5.0 # Apache-2.0