The last use of ecnt was in 12788ae4.  It was getting incremented after a
backend error without any purpose since then, so let's get rid of it.

Author: Kota Miyake
Reviewed-by: Álvaro Herrera
Discussion: https://postgr.es/m/786c3d9fbe067763d899e78c296f9f0f@oss.nttdata.com