Remove some unused and seldom used fields from RelationAmInfo.

This saves some memory from each index relcache entry. At least on a 64-bit
machine, it saves just enough to shrink a typical relcache entry's memory
usage from 2k to 1k. That's nice if you have a lot of backends and a lot of
indexes.
pgindent:  add newline to die() so script line number is not reported on failure.
doc: Update PQgetssl() documentation

The return type of PQgetssl() was changed from SSL* to void* a long time
ago, but the documentation was not updated.