Android builders do not need host toolchains.

This trims a few packages.  We do the same in buildbot.

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4634

Change-Id: I4c76d744917cb244ca3390d55d9ea602cda2dd58
Reviewed-on: https://skia-review.googlesource.com/4634
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@chromium.org>
diff --git a/infra/bots/gen_tasks.go b/infra/bots/gen_tasks.go
index 5796e04..fe69f35 100644
--- a/infra/bots/gen_tasks.go
+++ b/infra/bots/gen_tasks.go
@@ -206,15 +206,9 @@
 		} else {
 			pkgs = append(pkgs, b.MustGetCipdPackageFromAsset("android_ndk_linux"))
 		}
-	}
-
-	// Clang on Linux.
-	if strings.Contains(name, "Ubuntu") && strings.Contains(name, "Clang") {
+	} else if strings.Contains(name, "Ubuntu") && strings.Contains(name, "Clang") {
 		pkgs = append(pkgs, b.MustGetCipdPackageFromAsset("clang_linux"))
-	}
-
-	// Windows toolchain.
-	if strings.Contains(name, "Win") {
+	} else if strings.Contains(name, "Win") {
 		pkgs = append(pkgs, b.MustGetCipdPackageFromAsset("win_toolchain"))
 		if strings.Contains(name, "Vulkan") {
 			pkgs = append(pkgs, b.MustGetCipdPackageFromAsset("win_vulkan_sdk"))