internal: remove vulndb-v1 experiment

Remove logic to support the vulndb-v1 experiment, which is no longer
experimental.

Change-Id: I9db9658d8c747f42b889c7f90950400b31606dfd
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/484055
Reviewed-by: Julie Qiu <julieqiu@google.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: Tatiana Bradley <tatianabradley@google.com>
diff --git a/internal/experiment.go b/internal/experiment.go
index 5c2e1af..e2681b7 100644
--- a/internal/experiment.go
+++ b/internal/experiment.go
@@ -8,7 +8,6 @@
 const (
 	ExperimentEnableStdFrontendFetch = "enable-std-frontend-fetch"
 	ExperimentStyleGuide             = "styleguide"
-	ExperimentVulndbV1               = "vulndb-v1"
 )
 
 // Experiments represents all of the active experiments in the codebase and
@@ -16,7 +15,6 @@
 var Experiments = map[string]string{
 	ExperimentEnableStdFrontendFetch: "Enable frontend fetching for module std.",
 	ExperimentStyleGuide:             "Enable the styleguide.",
-	ExperimentVulndbV1:               "Use the v1 vulnerability database instead of the legacy database.",
 }
 
 // Experiment holds data associated with an experimental feature for frontend