...similar to what has been done for svx/sdtmfitm.hxx in
6a2ea81c "Remove unused ctors" and
68969cc6 "Consistency around SdrMetricItem."

(SdrEdgeLine1DeltaItem::Clone had been recently---and in retrospect needlessly
---introduced in 596ec6f5 "Missing
SdrEdgeLine1DeltaItem::Clone override" before
3efa3ad7 "SdrEdgreLine*DeltaItem::Put/QueryValue
are same as underlying" revealed that SdrEdgeLine1DeltaItem was a needless
derivation of SdrMetricItem.)

Change-Id: I154d32d46a7c01c792aa4e812cf576d4d749e0c9