[scanner] Remove superfluous cases from switch in ScanEscape

Change-Id: I4d774452e4537ba507bab87ac0a197d17a2f2862
Reviewed-on: https://chromium-review.googlesource.com/c/1494759Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59953}

src/parsing/scanner.cc

@@ -455,9 +455,6 @@ bool Scanner::ScanEscape() {
   }
 
   switch (c) {
-    case '\'':  // fall through
-    case '"' :  // fall through
-    case '\\': break;
     case 'b' : c = '\b'; break;
     case 'f' : c = '\f'; break;
     case 'n' : c = '\n'; break;