database/sql: remove unnecessary else conditions

database/sql: remove unnecessary else conditions

Fixes golint warning about "if block ends with a return statement,
so drop this else and outdent its block".

Change-Id: Iac4fd324e04e3e3fe3e3933f5e59095041d292c5
Reviewed-on: https://go-review.googlesource.com/107115
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Daniel Theophanes <kardianos@gmail.com>
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>