Drop support of Autoconf/Automake and QMake

PR #19335.

src/app/app.pri

@@ -1,25 +0,0 @@
-INCLUDEPATH += $$PWD
-
-HEADERS += \
-    $$PWD/application.h \
-    $$PWD/applicationinstancemanager.h \
-    $$PWD/cmdoptions.h \
-    $$PWD/filelogger.h \
-    $$PWD/qtlocalpeer/qtlocalpeer.h \
-    $$PWD/signalhandler.h \
-    $$PWD/upgrade.h
-
-SOURCES += \
-    $$PWD/application.cpp \
-    $$PWD/applicationinstancemanager.cpp \
-    $$PWD/cmdoptions.cpp \
-    $$PWD/filelogger.cpp \
-    $$PWD/main.cpp \
-    $$PWD/qtlocalpeer/qtlocalpeer.cpp \
-    $$PWD/signalhandler.cpp \
-    $$PWD/upgrade.cpp
-
-stacktrace {
-    HEADERS += $$PWD/stacktrace.h
-    SOURCES += $$PWD/stacktrace.cpp
-}