_content/security/vuln: remove mention of multiple dbs in docs

Change-Id: I2d298351c83a141e145e166a548e87276887968e
Reviewed-on: https://go-review.googlesource.com/c/website/+/485836
Run-TryBot: Tatiana Bradley <tatianabradley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Julie Qiu <julieqiu@google.com>
Reviewed-by: Tatiana Bradley <tatianabradley@google.com>

_content/security/vuln/database.md

@@ -41,11 +41,10 @@ so even a site serving from a fixed file system (including a file:// URL)
 can be a vulnerability database.
 
 By default, govulncheck uses the Go vulnerability database at [vuln.go.dev](https://vuln.go.dev).
-The command can be configured to contact vulnerability databases using the
+The command can be configured to contact a different vulnerability database using the
 GOVULNDB environment variable,
-which accepts a list of a comma-separated list of vulnerability database URLs,
-with http://, https://, or
-file:// protocols. Entries from multiple databases are merged.
+which accepts a vulnerability database URL with protocol `http://`, `https://`, or
+`file://`.
 
 The vulnerability database supports the endpoints listed below. For each path: