Remove a useless declaration: preload_characters cannot be > 4 as we have a Min() above

Bug: 
Change-Id: I553d6481a485a87c0246424270d63297400ceabe
Reviewed-on: https://chromium-review.googlesource.com/579909Reviewed-by: Yang Guo <yangguo@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49476}

AUTHORS

@@ -131,6 +131,7 @@ Sandro Santilli <strk@keybit.net>
 Sanjoy Das <sanjoy@playingwithpointers.com>
 Seo Sanghyeon <sanxiyn@gmail.com>
 Stefan Penner <stefan.penner@gmail.com>
+Sylvestre Ledru <sledru@mozilla.com>
 Tobias Burnus <burnus@net-b.de>
 Victor Costan <costan@gmail.com>
 Vlad Burlik <vladbph@gmail.com>

src/regexp/jsregexp.cc

@@ -3469,10 +3469,10 @@ void LoopChoiceNode::Emit(RegExpCompiler* compiler, Trace* trace) {
 int ChoiceNode::CalculatePreloadCharacters(RegExpCompiler* compiler,
                                            int eats_at_least) {
   int preload_characters = Min(4, eats_at_least);
+  DCHECK_LE(preload_characters, 4);
   if (compiler->macro_assembler()->CanReadUnaligned()) {
     bool one_byte = compiler->one_byte();
     if (one_byte) {
-      if (preload_characters > 4) preload_characters = 4;
       // We can't preload 3 characters because there is no machine instruction
       // to do that.  We can't just load 4 because we could be reading
       // beyond the end of the string, which could cause a memory fault.