Use version mutator for NDK

The ndk_api mutator is similar to the version mutator.  Move the
ndk_library ndk_api variations into the version mutator instead,
which will help later when consolidating the stubs handling
between NDK, LLDNK and Apex libraries.

Test: No change to build.ninja or Android-${TARGET_PRODUCT}.mk
Change-Id: I51417cf669265762c15f7289e1dc186d017ef4a9
diff --git a/cc/cc.go b/cc/cc.go
index 8235e35..2c5868b 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -1978,13 +1978,13 @@
 
 	ndkStubDepTag := libraryDependencyTag{Kind: sharedLibraryDependency, ndk: true, makeSuffix: "." + version}
 	actx.AddVariationDependencies([]blueprint.Variation{
-		{Mutator: "ndk_api", Variation: version},
+		{Mutator: "version", Variation: version},
 		{Mutator: "link", Variation: "shared"},
 	}, ndkStubDepTag, variantNdkLibs...)
 
 	ndkLateStubDepTag := libraryDependencyTag{Kind: sharedLibraryDependency, Order: lateLibraryDependency, ndk: true, makeSuffix: "." + version}
 	actx.AddVariationDependencies([]blueprint.Variation{
-		{Mutator: "ndk_api", Variation: version},
+		{Mutator: "version", Variation: version},
 		{Mutator: "link", Variation: "shared"},
 	}, ndkLateStubDepTag, variantLateNdkLibs...)