Revert of [turbofan] Relax effects and context for...

Revert of [turbofan] Relax effects and context for JSToNumber(x:plain-primitive). (patchset #1 id:1 of https://codereview.chromium.org/799413002/)

Reason for revert:
Performance regressions on primes and corrections benchmarks.

Original issue's description:
> [turbofan] Relax effects and context for JSToNumber(x:plain-primitive).
>
> TEST=unittests
> R=svenpanne@chromium.org
>
> Committed: https://chromium.googlesource.com/v8/v8/+/75484e8d16866eba7aa9c3b87841cd6ce2f466b8

TBR=svenpanne@chromium.org
NOTREECHECKS=true
NOTRY=true

Review URL: https://codereview.chromium.org/806103002

Cr-Commit-Position: refs/heads/master@{#25831}

src/compiler/js-typed-lowering.cc

@@ -18,6 +18,7 @@ namespace compiler {
 // TODO(turbofan): js-typed-lowering improvements possible
 // - immediately put in type bounds for all new nodes
 // - relax effects from generic but not-side-effecting operations
+// - relax effects for ToNumber(mixed)
 
 
 // Relax the effects of {node} by immediately replacing effect uses of {node}
@@ -730,9 +731,6 @@ Reduction JSTypedLowering::ReduceJSToNumber(Node* node) {
         node->ReplaceInput(i, value);
       }
       node->TrimInputCount(input_count);
-    } else {
-      // JSToNumber(x:plain-primitive,context) => JSToNumber(x,no-context)
-      node->ReplaceInput(1, jsgraph()->NoContextConstant());
     }
     return Changed(node);
   }

test/unittests/compiler/js-typed-lowering-unittest.cc

@@ -196,23 +196,6 @@ TEST_F(JSTypedLoweringTest, JSToBooleanWithSelect) {
 }
 
 
-// -----------------------------------------------------------------------------
-// JSToNumber
-
-
-TEST_F(JSTypedLoweringTest, JSToNumberWithPlainPrimitive) {
-  Node* const input = Parameter(Type::PlainPrimitive(), 0);
-  Node* const context = Parameter(Type::Any(), 1);
-  Node* const effect = graph()->start();
-  Node* const control = graph()->start();
-  Reduction r = Reduce(graph()->NewNode(javascript()->ToNumber(), input,
-                                        context, effect, control));
-  ASSERT_TRUE(r.Changed());
-  EXPECT_THAT(r.replacement(), IsToNumber(input, IsNumberConstant(0),
-                                          graph()->start(), control));
-}
-
-
 // -----------------------------------------------------------------------------
 // JSStrictEqual