Optimize buildPropFile()

Use android.WriteFileRuleVerbatim instead of a custom RuleBuilder
with echo commands.

Test: m nothing --no-skip-soong-tests
Change-Id: I9734305cbb404fd2ae841af2525f0db235622315
diff --git a/filesystem/filesystem.go b/filesystem/filesystem.go
index 6612a6f..795a0aa 100644
--- a/filesystem/filesystem.go
+++ b/filesystem/filesystem.go
@@ -311,18 +311,16 @@
 }
 
 func (f *filesystem) buildPropFile(ctx android.ModuleContext) (propFile android.OutputPath, toolDeps android.Paths) {
-	type prop struct {
-		name  string
-		value string
-	}
-
-	var props []prop
 	var deps android.Paths
+	var propFileString strings.Builder
 	addStr := func(name string, value string) {
-		props = append(props, prop{name, value})
+		propFileString.WriteString(name)
+		propFileString.WriteRune('=')
+		propFileString.WriteString(value)
+		propFileString.WriteRune('\n')
 	}
 	addPath := func(name string, path android.Path) {
-		props = append(props, prop{name, path.String()})
+		addStr(name, path.String())
 		deps = append(deps, path)
 	}
 
@@ -376,15 +374,7 @@
 		addStr("hash_seed", uuid)
 	}
 	propFile = android.PathForModuleOut(ctx, "prop").OutputPath
-	builder := android.NewRuleBuilder(pctx, ctx)
-	builder.Command().Text("rm").Flag("-rf").Output(propFile)
-	for _, p := range props {
-		builder.Command().
-			Text("echo").
-			Flag(`"` + p.name + "=" + p.value + `"`).
-			Text(">>").Output(propFile)
-	}
-	builder.Build("build_filesystem_prop", fmt.Sprintf("Creating filesystem props for %s", f.BaseModuleName()))
+	android.WriteFileRuleVerbatim(ctx, propFile, propFileString.String())
 	return propFile, deps
 }