Fix apparent SdrCaptionAngleItem vs. SdrCaptionFixedAngleItem mismatch

...though it was like that ever since fd069bee7e57ad529c3c0974559fd2d84ec3151a "initial import"

Change-Id: Ib3efe7bf7a559ede52966f4763a9f9e748b6ba6a
Consistency around SdrOnOffItem in svx/sxcaitm.hxx

...similar to what has been done for svx/sdtmfitm.hxx in
6a2ea81ca1622d2c2ad55bea8ddc28167fcc2794 "Remove unused ctors" and
68969cc61adecac481ae9656978ef952f435b310 "Consistency around SdrMetricItem."

Change-Id: I1a88c73c8e4c764a6beadb8bb54910d868a12d93