remove forgotten traces of Qt4 in configure script

config/lyxinclude.m4

@@ -63,7 +63,7 @@ AC_MSG_RESULT([$withval])
 ])
 
 
-dnl Check whether to configure for Qt4, Qt5, or Qt6. Default is Qt5.
+dnl Check whether to configure for Qt5, or Qt6. Default is Qt5.
 dnl
 AC_DEFUN([LYX_CHECK_QT6],[
 AC_MSG_CHECKING([whether Qt6 is requested])
@@ -404,10 +404,6 @@ if test x$GXX = xyes; then
       clang-3.0*|clang-3.1*|clang-3.2*|clang-3.3*)
         dnl boost contains pragmas that are annoying on older clang versions
         AM_CPPFLAGS="-Wno-unknown-pragmas $AM_CPPFLAGS";;
-      clang*)
-        dnl the more recent versions support the deprecated-register warning,
-        dnl which  is very annoying with Qt4.x right now.
-        AM_CXXFLAGS="$AM_CXXFLAGS -Wno-deprecated-register";;
     esac
 fi
 ])

config/qt.m4

@@ -128,7 +128,7 @@ dnl start here
 AC_DEFUN([QT_DO_IT_ALL],
 [
 	dnl this variable is precious
-	AC_ARG_VAR(QTDIR, [the place where the Qt files are, e.g. /usr/lib/qt4])
+	AC_ARG_VAR(QTDIR, [the place where the Qt files are, e.g. /usr/lib/qt5])
 
 	AC_ARG_WITH(qt-dir, [AS_HELP_STRING([--with-qt-dir], [where the root of Qt is installed])],
 		[ qt_cv_dir=`eval echo "$withval"/` ])
@@ -184,7 +184,7 @@ AC_DEFUN([QT_DO_IT_ALL],
 	fi
 
 	if test -z "$QT_LIB"; then
-	  dnl Try again with Qt5 and then Qt4 if configuring for Qt6/5 fails
+	  dnl Try again with Qt5 and if configuring for Qt6/5 fails
 	  if test x$USE_QT6 = xyes ; then
 		USE_QT6=no
 		AC_SUBST([USE_QT6])

development/Makefile.am

@@ -176,7 +176,6 @@ cmake/modules/FindLyXGettext.cmake \
 cmake/modules/FindMagic.cmake \
 cmake/modules/FindMYTHESLIB.cmake \
 cmake/modules/FindOpenSSL.cmake \
-cmake/modules/FindQt4.cmake \
 cmake/modules/FindZLIB.cmake \
 cmake/modules/LyXDestinations.cmake \
 cmake/modules/LyXMacros.cmake \