[Interpreter] Pops the context to the correct level on return.

test/cctest/interpreter/bytecode_expectations/ContextVariables.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: mixed
 execute: yes
 wrap: yes
 
 ---
@@ skipping 88 matching lines @@
 ]
 
 ---
 snippet: "
   'use strict';
   let a = 1;
   { let b = 2; return function() { a + b; }; }
 "
 frame size: 4
 parameter count: 1
-bytecode array length: 45
+bytecode array length: 47
 bytecodes: [
   B(CallRuntime), U16(Runtime::kNewFunctionContext), R(closure), U8(1),
   B(PushContext), R(0),
   B(LdaTheHole),
   B(StaContextSlot), R(context), U8(4),
   B(StackCheck),
   B(LdaSmi8), U8(1),
   B(StaContextSlot), R(context), U8(4),
   B(LdaConstant), U8(0),
   B(Star), R(2),
   B(Ldar), R(closure),
   B(Star), R(3),
   B(CallRuntime), U16(Runtime::kPushBlockContext), R(2), U8(2),
   B(PushContext), R(1),
   B(LdaTheHole),
   B(StaContextSlot), R(context), U8(4),
   B(LdaSmi8), U8(2),
   B(StaContextSlot), R(context), U8(4),
   B(CreateClosure), U8(1), U8(0),
+  B(PopContext), R(0),
   B(Return),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,
   InstanceType::SHARED_FUNCTION_INFO_TYPE,
 ]
 handlers: [
 ]
 
 ---
@@ skipping 772 matching lines @@
   B(StaContextSlotWide), R(context), U16(256),
   B(LdaContextSlotWide), R(context), U16(256),
   B(Return),
 ]
 constant pool: [
   InstanceType::ONE_BYTE_INTERNALIZED_STRING_TYPE,
 ]
 handlers: [
 ]