[Interpreter] Replace BytecodeRegisterAllocator with a simple bump pointer.

test/cctest/interpreter/bytecode_expectations/LetVariable.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 execute: yes
 wrap: yes
 
 ---
 snippet: "
@@ skipping 40 matching lines @@
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   let x = (x = 20);
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 26
+bytecode array length: 29
 bytecodes: [
                 B(LdaTheHole),
                 B(Star), R(0),
   /*   30 E> */ B(StackCheck),
   /*   45 S> */ B(LdaSmi), U8(20),
                 B(Star), R(1),
                 B(Ldar), R(0),
                 B(JumpIfNotHole), U8(11),
                 B(LdaConstant), U8(0),
                 B(Star), R(2),
   /*   45 E> */ B(CallRuntime), U16(Runtime::kThrowReferenceError), R(2), U8(1),
                 B(Mov), R(1), R(0),
+                B(Mov), R(1), R(0),
                 B(LdaUndefined),
   /*   52 S> */ B(Return),
 ]
 constant pool: [
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["x"],
 ]
 handlers: [
 ]
 
 ---
@@ skipping 19 matching lines @@
                 B(Mov), R(1), R(0),
                 B(LdaUndefined),
   /*   54 S> */ B(Return),
 ]
 constant pool: [
   ONE_BYTE_INTERNALIZED_STRING_TYPE ["x"],
 ]
 handlers: [
 ]