libc_malloc_[debug|hooks] are not available for platform

The libs are not available for platform. Thus removing
'//apex_available:platform' from the apex_available property. However,
since there are test modules that statically links the libs, we
exceptionally make the static variant of the libs available to the
platform.

Test: m
Test: mm under bionic does not create
out/target/product/<name>/system/lib[64]/libc_malloc_[debug|hooks].so

Change-Id: Ia6d473658c4231b04b5db511f9dacbbdf0f207b0
diff --git a/libc/malloc_hooks/Android.bp b/libc/malloc_hooks/Android.bp
index a0f8102..861c371 100644
--- a/libc/malloc_hooks/Android.bp
+++ b/libc/malloc_hooks/Android.bp
@@ -32,6 +32,15 @@
         "-Werror",
         "-fno-stack-protector",
     ],
+
+    apex_available: [
+        "com.android.runtime",
+    ],
+    static: {
+        apex_available: [
+            "//apex_available:platform",
+        ],
+    },
 }
 
 // ==============================================================