Marco Trevisan authored Jan 27, 2020 and Bastien Nocera committed Feb 05, 2020

There's no need to declare it as extern in the header as it is already
declared in the source files where it's used.

Fixes:
../src/device.c:51:25: error: redundant redeclaration of ‘fprintd_dbus_conn’ [-Werror=redundant-decls]
  51 | extern DBusGConnection *fprintd_dbus_conn;
     |                         ^~~~~~~~~~~~~~~~~
In file included from ../src/device.c:34:
../src/fprintd.h:29:25: note: previous declaration of ‘fprintd_dbus_conn’ was here
  29 | extern DBusGConnection *fprintd_dbus_conn;
     |                         ^~~~~~~~~~~~~~~~~