Refactor some tests to not use bp2build_avail

Bug: 301312260
Test: presubmits
Change-Id: I67ca45f17d11e9b893fae5f6c6df1239ae4220b6
diff --git a/bp2build/cc_library_conversion_test.go b/bp2build/cc_library_conversion_test.go
index ec603c2..2cbcfc1 100644
--- a/bp2build/cc_library_conversion_test.go
+++ b/bp2build/cc_library_conversion_test.go
@@ -1857,7 +1857,6 @@
 		Blueprint: soongCcLibraryPreamble + `
 cc_library {
 	name: "libc_musl",
-	bazel_module: { bp2build_available: false },
 }
 
 cc_library {
@@ -1912,10 +1911,10 @@
 		Description:                "cc_library system_shared_lib empty for linux_musl variant",
 		ModuleTypeUnderTest:        "cc_library",
 		ModuleTypeUnderTestFactory: cc.LibraryFactory,
+		StubbedBuildDefinitions:    []string{"libc_musl"},
 		Blueprint: soongCcLibraryPreamble + `
 cc_library {
 		name: "libc_musl",
-		bazel_module: { bp2build_available: false },
 }
 
 cc_library {