internal/postgres: cascade when truncating paths table
internal/postgres: cascade when truncating paths table

When truncating the paths table in tests, deletions are now cascaded.

This is needed for migration 000062 to pass.

Change-Id: I340add1ee7d182290866c6deafdd27defc1ba9b6
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/289729
Trust: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Run-TryBot: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite