Remove __sh__ from atomic.cc

Missed in https://googleplex-android-review.googlesource.com/223277

Change-Id: I9dbbcaeeec7ff1f0a750cff1b89b60edf8cec142
diff --git a/src/atomic.cc b/src/atomic.cc
index fb4de9c..2638b21 100644
--- a/src/atomic.cc
+++ b/src/atomic.cc
@@ -49,9 +49,6 @@
 #define NEED_PTHREADS_QUASI_ATOMICS 1
 #endif
 
-#elif defined(__sh__)
-#define NEED_PTHREADS_QUASI_ATOMICS 1
-
 #else
 #error "QuasiAtomic unsupported on this platform"
 #endif