add bp2build subevents

Test: verified new events in bp2build_metrics.pb
Bug: 286412441
Change-Id: Ib803c3a3d1a8e7eaae5fb4c01c7769a72f4664ff
diff --git a/cmd/soong_build/main.go b/cmd/soong_build/main.go
index 62b3333..20e366e 100644
--- a/cmd/soong_build/main.go
+++ b/cmd/soong_build/main.go
@@ -814,9 +814,7 @@
 		// Run the code-generation phase to convert BazelTargetModules to BUILD files
 		// and print conversion codegenMetrics to the user.
 		codegenContext := bp2build.NewCodegenContext(ctx.Config(), ctx, bp2build.Bp2Build, topDir)
-		ctx.EventHandler.Do("codegen", func() {
-			codegenMetrics = bp2build.Codegen(codegenContext)
-		})
+		codegenMetrics = bp2build.Codegen(codegenContext)
 
 		ninjaDeps = append(ninjaDeps, codegenContext.AdditionalNinjaDeps()...)