Remove some unneeded dashes from libpq comments.

src/interfaces/libpq/fe-auth.c

src/interfaces/libpq/fe-connect.c

src/interfaces/libpq/fe-exec.c

src/interfaces/libpq/fe-lobj.c

src/interfaces/libpq/fe-misc.c

src/interfaces/libpq/pqexpbuffer.c