Drop obsolete libgtk2.0-dev and libglade2-dev from Build-Depends

Jeremy Bícharequested to merge
jbicha/qalculate-gtk:drop-obsolete-build-depends into debian/master

libglade2 is a helper library for GTK2 and GNOME 2.

Since qalculate has been ported to GTK3, the gtk2 and libglade2 Build-Depends are unused.

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