Remove dependencies on the 1-variant fallback

When adding a dependencies, if the variants don't match, but the
dependency only has 1 variant anyways, soong will always use that
variant. This makes it hard to add new variants to soong, because the
1-variant fallback stops being used and you start getting missing
variant errors. Make changes to bp files such that all dependencies
correctly specify the variant to use.

Bug: 372091092
Flag: EXEMPT refactor
Test: m nothing
Change-Id: I0bd19892e7ad88d9259a3c2031e92b90ac530e1c
diff --git a/tests/vendor_images/Android.bp b/tests/vendor_images/Android.bp
index 66f0219..0430eaa 100644
--- a/tests/vendor_images/Android.bp
+++ b/tests/vendor_images/Android.bp
@@ -2,19 +2,13 @@
     default_applicable_licenses: ["Android-Apache-2.0"],
 }
 
-prebuilt_etc {
-    name: "vendor_sign_key",
-    src: ":avb_testkey_rsa4096",
-    installable: false,
-}
-
 android_filesystem {
     name: "test_microdroid_vendor_image",
     partition_name: "microdroid-vendor",
     type: "ext4",
     file_contexts: ":microdroid_vendor_file_contexts.gen",
     use_avb: true,
-    avb_private_key: ":vendor_sign_key",
+    avb_private_key: ":avb_testkey_rsa4096",
     rollback_index: 5,
 }
 
@@ -24,7 +18,7 @@
     type: "ext4",
     file_contexts: ":microdroid_vendor_file_contexts.gen",
     use_avb: true,
-    avb_private_key: ":vendor_sign_key",
+    avb_private_key: ":avb_testkey_rsa4096",
 }
 
 android_filesystem {