[runtime] Remove unused %NumberUnaryMinus runtime function.

This has been dead code for quite a while now.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/1314353006

Cr-Commit-Position: refs/heads/master@{#30652}

src/runtime/runtime-numbers.cc

@@ -250,15 +250,6 @@ RUNTIME_FUNCTION(Runtime_NumberMul) {
 }
 
 
-RUNTIME_FUNCTION(Runtime_NumberUnaryMinus) {
-  HandleScope scope(isolate);
-  DCHECK(args.length() == 1);
-
-  CONVERT_DOUBLE_ARG_CHECKED(x, 0);
-  return *isolate->factory()->NewNumber(-x);
-}
-
-
 RUNTIME_FUNCTION(Runtime_NumberDiv) {
   HandleScope scope(isolate);
   DCHECK(args.length() == 2);

src/runtime/runtime.h

@@ -408,7 +408,6 @@ namespace internal {
   F(NumberAdd, 2, 1)                   \
   F(NumberSub, 2, 1)                   \
   F(NumberMul, 2, 1)                   \
-  F(NumberUnaryMinus, 1, 1)            \
   F(NumberDiv, 2, 1)                   \
   F(NumberMod, 2, 1)                   \
   F(NumberImul, 2, 1)                  \