Bug#883304: qtbase-opensource-src Build-Depends libpcre3-dev, but uses bundled PCRE2 instead

[Anders Kaseorg <andersk@mit.edu>]

Source: qtbase-opensource-src
Version: 5.9.2+dfsg-4

Qt 5.9 swiched from the original PCRE to the newer PCRE2, but the build 
dependencies in qtbase-opensource-src were not adjusted.  So now 
qtbase-opensource-src has an unused build dependency on libpcre3-dev, and 
builds with a bundled copy of PCRE2 instead.  

The libpcre3-dev build dependency should be removed, and perhaps replaced 
with libpcre2-dev to pick up the system PCRE2.  Note that Debian’s pcre2 
10.22 is the same version as that bundled with Qt 5.9, but older than 
pcre2 10.30 bundled with Qt 5.10: https://bugs.debian.org/883224.