Revert "internal/postgres: utilize num_imports column in insert_module"

This reverts commit 28eed86.

Reason for revert: migration takes too long

Change-Id: I279e62342c79d2604cda4e7c9819bdaa8aac752c
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/721101
LUCI-TryBot-Result: Go LUCI <[email protected]>
kokoro-CI: kokoro <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: ethanalee-work

internal/postgres/insert_module.go

@@ -409,7 +409,6 @@ func (pdb *DB) insertUnits(ctx context.Context, tx *database.DB,
 			pq.Array(licenseTypes),
 			pq.Array(licensePaths),
 			pdb.bypassLicenseCheck || u.IsRedistributable,
-			len(u.Imports),
 		)
 		if u.Readme != nil {
 			pathToReadme[u.Path] = u.Readme
@@ -482,7 +481,6 @@ func insertUnits(ctx context.Context, db *database.DB, unitValues []any) (pathID
 		"license_types",
 		"license_paths",
 		"redistributable",
-		"num_imports",
 	}
 	uniqueUnitCols := []string{"path_id", "module_id"}
 	returningUnitCols := []string{"id", "path_id"}

internal/postgres/insert_module_test.go

@@ -124,7 +124,6 @@ func checkModule(ctx context.Context, t *testing.T, db *DB, want *internal.Modul
 			}
 		}
 		wantu.Subdirectories = subdirectories
-		wantu.NumImports = len(wantu.Imports)
 		opts := cmp.Options{
 			cmpopts.EquateEmpty(),
 			cmpopts.IgnoreFields(licenses.Metadata{}, "Coverage"),

internal/postgres/unit.go

@@ -474,7 +474,12 @@ func (db *DB) getUnitWithAllFields(ctx context.Context, um *internal.UnitMeta, b
 			r.contents,
 			d.synopsis,
 			d.source,
-			u.num_imports,
+			COALESCE((
+				SELECT COUNT(unit_id)
+				FROM imports
+				WHERE unit_id = u.id
+				GROUP BY unit_id
+				), 0) AS num_imports,
 			COALESCE((
 				SELECT imported_by_count
 				FROM search_documents