Remove USE_BAZEL and its dead code

This environment variable has been out of use for some time. It used to
control Bazel-as-executor, which has been removed from Bazel for several
releases.

Bug: 243077098
Test: Treehugger
Change-Id: I4edfb5f3574c369a16547ea06ba780293c37ecb3
diff --git a/ui/build/config.go b/ui/build/config.go
index 590aeb9..14a99d0 100644
--- a/ui/build/config.go
+++ b/ui/build/config.go
@@ -99,15 +99,9 @@
 
 	pathReplaced bool
 
-	// TODO(b/243077098): Remove useBazel.
-	useBazel      bool
 	bazelProdMode bool
 	bazelDevMode  bool
 
-	// During Bazel execution, Bazel cannot write outside OUT_DIR.
-	// So if DIST_DIR is set to an external dir (outside of OUT_DIR), we need to rig it temporarily and then migrate files at the end of the build.
-	riggedDistDirForBazel string
-
 	// Set by multiproduct_kati
 	emptyNinjaFile bool
 
@@ -439,21 +433,6 @@
 		ctx.Fatalf("Unable to remove bazel profile directory %q: %v", bpd, err)
 	}
 
-	ret.useBazel = ret.environ.IsEnvTrue("USE_BAZEL")
-
-	if ret.UseBazel() {
-		if err := os.MkdirAll(bpd, 0777); err != nil {
-			ctx.Fatalf("Failed to create bazel profile directory %q: %v", bpd, err)
-		}
-	}
-
-	if ret.UseBazel() {
-		ret.riggedDistDirForBazel = filepath.Join(ret.OutDir(), "dist")
-	} else {
-		// Not rigged
-		ret.riggedDistDirForBazel = ret.distDir
-	}
-
 	c := Config{ret}
 	storeConfigMetrics(ctx, c)
 	return c
@@ -486,7 +465,6 @@
 		ForceUseGoma:    proto.Bool(config.ForceUseGoma()),
 		UseGoma:         proto.Bool(config.UseGoma()),
 		UseRbe:          proto.Bool(config.UseRBE()),
-		BazelAsNinja:    proto.Bool(config.UseBazel()),
 		BazelMixedBuild: proto.Bool(config.BazelBuildEnabled()),
 	}
 	c.Targets = append(c.Targets, config.arguments...)
@@ -877,11 +855,7 @@
 }
 
 func (c *configImpl) DistDir() string {
-	if c.UseBazel() {
-		return c.riggedDistDirForBazel
-	} else {
-		return c.distDir
-	}
+	return c.distDir
 }
 
 func (c *configImpl) RealDistDir() string {
@@ -1129,11 +1103,6 @@
 	return false
 }
 
-// TODO(b/243077098): Remove UseBazel.
-func (c *configImpl) UseBazel() bool {
-	return c.useBazel
-}
-
 func (c *configImpl) BazelBuildEnabled() bool {
 	return c.bazelProdMode || c.bazelDevMode
 }