Windows: Remove support for QT_QPA_VERBOSE logging environment variable

We have QT_LOGGING_RULES nowadays, and the verbosity levels for
QWindowsContext are controlled by the `verbose` platform plugin
argument.

Change-Id: I3f998afaa962220b7babb093c030d0798e450db0
Reviewed-by: Kai Köhne <kai.koehne@qt.io>
Reviewed-by: Zhao Yuhang <2546789017@qq.com>
Reviewed-by: Wladimir Leuschner <wladimir.leuschner@qt.io>

src/plugins/platforms/windows/main.cpp

@@ -25,17 +25,9 @@ using namespace Qt::StringLiterals;
     \li \c fontengine=native Indicates that native font engine should be used (default)
     \li \c fontengine=freetype Indicates that freetype font engine should be used
     \li \c gl=gdi Indicates that ARB Open GL functionality should not be used
+    \li \c verbose=<number> Chooses the verbosity level of the platform plugin logging (0-9).
     \endlist
 
-    \section1 Tips
-
-    \list
-    \li The environment variable \c QT_QPA_VERBOSE controls
-       the debug level. It takes the form
-       \c{<keyword1>:<level1>,<keyword2>:<level2>}, where
-       keyword is one of \c integration, \c windows, \c backingstore and
-       \c fonts. Level is an integer 0..9.
-    \endlist
     \internal
  */
 

src/plugins/platforms/windows/qwindowscontext.cpp

@@ -181,10 +181,6 @@ QWindowsContext::QWindowsContext() :
 #    pragma warning( disable : 4996 )
 #endif
     m_instance = this;
-    // ### FIXME: Remove this once the logging system has other options of configurations.
-    const QByteArray bv = qgetenv("QT_QPA_VERBOSE");
-    if (!bv.isEmpty())
-        QLoggingCategory::setFilterRules(QString::fromLocal8Bit(bv));
 }
 
 QWindowsContext::~QWindowsContext()

src/plugins/platforms/windows/qwindowscontext.h

@@ -56,7 +56,7 @@ public:
         SI_SupportsTouch = 0x2
     };
 
-    // Verbose flag set by environment variable QT_QPA_VERBOSE
+    // Verbose flag set by the `verbose` platform plugin argument
     static int verbose;
 
     explicit QWindowsContext();