Remove register specifier removed from C++17
gcc11 defaults to -std=gnu++17, which warns:
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/eggcellrendererkeys.cc:139:56: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/eggcellrendererkeys.cc:140:25: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/eggcellrendererkeys.cc:141:23: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/eggcellrendererkeys.cc:141:30: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/gnome-cmd-file-list.cc:390:25: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/gnome-cmd-file-list.cc:391:23: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/gnome-cmd-file-list.cc:391:30: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
/builddir/build/BUILD/GIT/gnome-commander/_BUILDDIR/../src/gnome-cmd-file-list.cc:411:49: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]Just remove these deprecated specifier.