[arm64] Fixed unnecessary environment assignment to LSmiTag instruction.

test/mjsunit/regress/regress-crbug-490021.js

Index: test/mjsunit/regress/regress-crbug-490021.js
diff --git a/test/mjsunit/regress/regress-filter-contexts.js b/test/mjsunit/regress/regress-crbug-490021.js
similarity index 75%
copy from test/mjsunit/regress/regress-filter-contexts.js
copy to test/mjsunit/regress/regress-crbug-490021.js
index d2abe0032548428324afd6675a7031bf53a5e56e..745c0a801051037274b6f1e52de5a8ed92d98a86 100644
--- a/test/mjsunit/regress/regress-filter-contexts.js
+++ b/test/mjsunit/regress/regress-crbug-490021.js
@@ -4,9 +4,10 @@
 
 // Flags: --allow-natives-syntax
 
-function f() { return f.x; }
-f.__proto__ = null;
-f.prototype = "";
+var global = new Object(3);
+function f() {
+  global[0] = global[0] >>> 15.5;
+}
 
 f();
 f();