Switch platform EH unwinder to prebuilt LLVM libunwind

For the platform libc++ STL, remove the
-Wl,--exclude-libs,libunwind_llvm.a argument, which is redundant with
the same argument in deviceGlobalLdflags.

Bug: http://b/153025717
Test: device boots
Change-Id: Idd7791d52f74aab2d5f59419fb75f841fc29a2eb
diff --git a/apex/apex.go b/apex/apex.go
index 5cd18ed..bff7793 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -2854,7 +2854,7 @@
 		"libprofile-clang-extras_ndk",
 		"libprofile-extras",
 		"libprofile-extras_ndk",
-		"libunwind_llvm",
+		"libunwind",
 	}
 	return m
 }