Re-enable the POSIX header tests for musl.

Bug: http://b/265874089
Test: treehugger
Change-Id: I05892d4a57fcceab0322c910d6482929b82bc5ee
diff --git a/tests/headers/posix/Android.bp b/tests/headers/posix/Android.bp
index 4a20d45..0809cdb 100644
--- a/tests/headers/posix/Android.bp
+++ b/tests/headers/posix/Android.bp
@@ -33,8 +33,5 @@
         darwin: {
             enabled: false,
         },
-        musl: {
-            enabled: false,
-        },
     },
 }