Edit info about the configuration system

Remove an obsolete note and move the description of the
-developer-build option to its own section, now that it
is not mentioned in the topic about -prefix builds any more.

Fixes: QTBUG-63017
Change-Id: Icd4f4477278990bb76b8862a6c0b5632090095bf
Reviewed-by: Paul Wicking <paul.wicking@qt.io>

doc/src/configure.qdoc

 /****************************************************************************
 **
-** Copyright (C) 2017 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the documentation of the Qt Toolkit.
@@ -80,15 +80,6 @@
     make install
     \endcode
 
-    \note The 'make install' step is required only if Qt is configured with a
-    \e -prefix, which is the default on Unix-based platforms unless the
-    \e -developer-build configure option is used. On Windows, Qt is configured
-    as a non-prefix build by default.
-
-    \note The \c -developer-build is meant for developing Qt and not for
-    shipping applications. Such a build contains more exported symbols than
-    a standard build and compiles with a higher warning level.
-
     \section1 Modules and Features
 
     Qt consists of different \l{All Modules}{modules} whose sources can be
@@ -281,4 +272,10 @@
     dynamically switch between the available options at runtime. For more
     details about the benefits of using dynamic GL-switching, see
     \l{Graphics Drivers}.
+
+    \section1 Developer Builds
+
+    The \c -developer-build option is not meant for shipping applications,
+    but can be used for developing Qt. Such a build contains more exported
+    symbols than a standard build and compiles with a higher warning level.
 */