Remove support for Object.observe

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 222aac4328367b4a02630e197a19af3eb02c2e9d..cce4395bcfe761eca17ad6d1ee33707f0027c16c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -286,7 +286,6 @@ action("js2c") {
     "src/js/arraybuffer.js",
     "src/js/typedarray.js",
     "src/js/iterator-prototype.js",
-    "src/js/object-observe.js",
     "src/js/collection.js",
     "src/js/weak-collection.js",
     "src/js/collection-iterator.js",
@@ -342,7 +341,6 @@ action("js2c_experimental") {
     "src/messages.h",
     "src/js/harmony-atomics.js",
     "src/js/harmony-regexp-exec.js",
-    "src/js/harmony-object-observe.js",
     "src/js/harmony-sharedarraybuffer.js",
     "src/js/harmony-simd.js",
     "src/js/harmony-species.js",
@@ -1328,7 +1326,6 @@ source_set("v8_base") {
     "src/runtime/runtime-maths.cc",
     "src/runtime/runtime-numbers.cc",
     "src/runtime/runtime-object.cc",
-    "src/runtime/runtime-observe.cc",
     "src/runtime/runtime-operators.cc",
     "src/runtime/runtime-proxy.cc",
     "src/runtime/runtime-regexp.cc",