Drop unused BuildRequires: pkgconfig(dbus-glib-1)

...which had originally been added with 38ee1f0e29
"add missing build dep", but without any further information.  (And then changed
from an explicit dbus-glib-devel to the current pkconfig(dbus-glib-1) in
fb9ee009ae "update build deps to Packaging
Guidelines".)  But it appears to be completely unused by now.

libreoffice.spec

@@ -147,7 +147,6 @@ BuildRequires: lpsolve-devel
 BuildRequires: openldap-devel
 BuildRequires: pam-devel
 BuildRequires: pkgconfig(bluez)
-BuildRequires: pkgconfig(dbus-glib-1)
 BuildRequires: pkgconfig(dconf)
 BuildRequires: pkgconfig(epoxy)
 BuildRequires: pkgconfig(evolution-data-server-1.2)