Remove yet-unused 64-bit atomic hooks.

include/core/SkThread.h

Index: include/core/SkThread.h
diff --git a/include/core/SkThread.h b/include/core/SkThread.h
index 403b288f19087bcf7b48729d3d3f3a38b0af480d..c8f13a709263f92736c0bebcac1687691cd838ce 100644
--- a/include/core/SkThread.h
+++ b/include/core/SkThread.h
@@ -22,20 +22,17 @@ static int64_t sk_atomic_inc(int64_t* addr);
  *  No additional memory barrier is required; this must act as a compiler barrier.
  */
 static int32_t sk_atomic_add(int32_t* addr, int32_t inc);
-static int64_t sk_atomic_add(int64_t* addr, int64_t inc);
 
 /** Atomically subtracts one from the int referenced by addr and returns the previous value.
  *  This must act as a release (SL/S) memory barrier and as a compiler barrier.
  */
 static int32_t sk_atomic_dec(int32_t* addr);
-static int64_t sk_atomic_dec(int64_t* addr);
 
 /** Atomic compare and set.
  *  If *addr == before, set *addr to after and return true, otherwise return false.
  *  This must act as a release (SL/S) memory barrier and as a compiler barrier.
  */
 static bool sk_atomic_cas(int32_t* addr, int32_t before, int32_t after);
-static bool sk_atomic_cas(int64_t* addr, int64_t before, int64_t after);
 
 /** If sk_atomic_dec does not act as an acquire (L/SL) barrier,
  *  this must act as an acquire (L/SL) memory barrier and as a compiler barrier.