Drop bootstrap.ninja.d

This also shaves off a couple seconds from the build.

Test: `time m nothing` 2 times with and without the change
Bug: 243699430
Change-Id: I5cc5cba2b98c845ddd6ba7c3b31ad678451afe41
diff --git a/ui/build/soong.go b/ui/build/soong.go
index 3920ddd..e445ad4 100644
--- a/ui/build/soong.go
+++ b/ui/build/soong.go
@@ -32,7 +32,6 @@
 
 	"github.com/google/blueprint"
 	"github.com/google/blueprint/bootstrap"
-	"github.com/google/blueprint/deptools"
 	"github.com/google/blueprint/microfactory"
 
 	"google.golang.org/protobuf/proto"
@@ -344,12 +343,9 @@
 			soongDocsInvocation},
 	}
 
-	bootstrapDeps := bootstrap.RunBlueprint(blueprintArgs, bootstrap.DoEverything, blueprintCtx, blueprintConfig)
-	bootstrapDepFile := shared.JoinPath(config.SoongOutDir(), "bootstrap.ninja.d")
-	err := deptools.WriteDepFile(bootstrapDepFile, blueprintArgs.OutFile, bootstrapDeps)
-	if err != nil {
-		ctx.Fatalf("Error writing depfile '%s': %s", bootstrapDepFile, err)
-	}
+	// since `bootstrap.ninja` is regenerated unconditionally, we ignore the deps, i.e. little
+	// reason to write a `bootstrap.ninja.d` file
+	_ = bootstrap.RunBlueprint(blueprintArgs, bootstrap.DoEverything, blueprintCtx, blueprintConfig)
 }
 
 func checkEnvironmentFile(currentEnv *Environment, envFile string) {