Install charmaps uncompressed in testroot

The testroot does not have a gunzip command, so the charmap files
should not be installed gzipped else they cannot be used (and thus
tested).  With this patch, installing with INSTALL_UNCOMPRESSED=yes
installs uncompressed charmaps instead.

Note that we must purge the $(symbolic_link_list) as it contains
references to $(DESTDIR), which we change during the testroot
installation.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>