Remove extern "C" warpper around atspi/glib headers inclusion

Recently glib headers started using C++ features when compled in C++ glib!1715 (commits)

This leads to errors like: .. In file included from /usr/include/glib-2.0/glib/gatomic.h:31, from /usr/include/glib-2.0/glib/gthread.h:32, from /usr/include/glib-2.0/glib/gasyncqueue.h:32, from /usr/include/glib-2.0/glib.h:32, from /usr/include/at-spi-2.0/atspi/atspi.h:27, from dasher_editor_external_atspi.cpp:5: /usr/include/c++/11/type_traits:56:3: error: template with C linkage 56 | template<typename _Tp, _Tp __v> | ^~~~~~~~ dasher_editor_external_atspi.cpp:4:1: note: 'extern "C"' linkage started here 4 | extern "C" { | ^~~~~~~~~~ ..

Since for a while now glib headers are supposed to be safe to include in C++ code without extern "C" just remove it.