internal/report: drop requirement that 'published' field be set

We now populate the published field from the git history, so this
field only needs to be set when that history should be overridden.

For golang/vulndb#50434

Change-Id: If496f753ddf9b23b8bb0fcb462a096298f516966
Reviewed-on: https://go-review.googlesource.com/c/vulndb/+/376614
Trust: Damien Neil <dneil@google.com>
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/internal/report/lint.go b/internal/report/lint.go
index 0e9b766..0633b7c 100644
--- a/internal/report/lint.go
+++ b/internal/report/lint.go
@@ -243,10 +243,6 @@
 		addIssue("missing description")
 	}
 
-	if r.Published.IsZero() {
-		addIssue("missing published")
-	}
-
 	if r.LastModified != nil && r.LastModified.Before(r.Published) {
 		addIssue("last_modified is before published")
 	}