internal/frontend: don't fetch licenses in fetchMainDetails

We don't need licenses in fetchMainDetails. GetUnit is now called only
with the relevant fields.

Change-Id: I7a1558fa10bc88c246b028c467cfee01b4d681fd
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/262102
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
diff --git a/internal/frontend/unit_main.go b/internal/frontend/unit_main.go
index 549de42..f43aa68 100644
--- a/internal/frontend/unit_main.go
+++ b/internal/frontend/unit_main.go
@@ -79,7 +79,7 @@
 }
 
 func fetchMainDetails(ctx context.Context, ds internal.DataSource, um *internal.UnitMeta, expandReadme bool) (_ *MainDetails, err error) {
-	unit, err := ds.GetUnit(ctx, um, internal.AllFields)
+	unit, err := ds.GetUnit(ctx, um, internal.WithReadme|internal.WithDocumentation|internal.WithSubdirectories|internal.WithImports)
 	if err != nil {
 		return nil, err
 	}