Remove unused libm_clang variable.

Bug: http://b/21899249

As part of the cleanup here, this unset/unused variable was missed.

Change-Id: I0e0f2640e2e975f3e154f68509aa791fd22053a9
diff --git a/libm/Android.mk b/libm/Android.mk
index ea5e72c..7e0656d 100644
--- a/libm/Android.mk
+++ b/libm/Android.mk
@@ -467,7 +467,6 @@
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/upstream-freebsd/lib/msun/src/
 LOCAL_C_INCLUDES_64 += $(LOCAL_PATH)/upstream-freebsd/lib/msun/ld128/
 
-LOCAL_CLANG := $(libm_clang)
 LOCAL_ARM_MODE := arm
 LOCAL_CFLAGS := \
     -D__BIONIC_NO_MATH_INLINES \
@@ -522,7 +521,6 @@
 
 
 LOCAL_MODULE := libm
-LOCAL_CLANG := $(libm_clang)
 LOCAL_SYSTEM_SHARED_LIBRARIES := libc
 LOCAL_WHOLE_STATIC_LIBRARIES := libm