fdo#63154 Removed unused solar.h reference in chart2

Change-Id: I4a16cd5492ced3c067fb037f31cb74a6d8068de1
Reviewed-on: https://gerrit.libreoffice.org/7603
Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>