Fix prototypes so they don't look like function definitions.

src/include/access/genam.h

src/include/access/gist.h

src/include/access/gistscan.h

src/include/access/giststrat.h

src/include/access/hash.h

src/include/access/heapam.h

src/include/access/hio.h

src/include/access/iqual.h

src/include/access/istrat.h

src/include/access/itup.h

src/include/access/nbtree.h

src/include/access/rtree.h

src/include/access/rtstrat.h

src/include/access/skey.h

src/include/access/transam.h

src/include/access/tupdesc.h

src/include/bootstrap/bootstrap.h

src/include/c.h

src/include/catalog/heap.h

src/include/catalog/index.h