Revert "Temp fix for regex_match offset capture issue"

This reverts commit c1aa8dd.

patched in OSS HHVM 3.29

Author: fredemmott

src/regex/private.php

@@ -47,8 +47,7 @@ function regex_match<T as Regex\Match>(
   if ($status === 1) {
     $match_out = darray[];
     foreach ($match as $key => $value) {
-      // TODO(T35726135) remove when HHVM fix is released.
-      $match_out[$key] = $value is string ? $value : $value[0];
+      $match_out[$key] = $value[0];
     }
     $offset_out = $match[0][1];
     /* HH_FIXME[4110] Native function won't have this problem */

tests/regex/RegexTest.php

@@ -184,13 +184,13 @@ public static function provideEveryMatch(
         darray[0 => 't1', 1 => '1'],
         darray[0 => 'e2', 1 => '2'],
         darray[0 => 's3', 1 => '3'],
-        darray[0 => 't', 1 => ''],
+        darray[0 => 't'],
       ]),
       tuple('t1e2s3t', re"/[a-z](?P<digit>\d)?/", 0, vec[
         darray[0 => 't1', 'digit' => '1', 1 => '1'],
         darray[0 => 'e2', 'digit' => '2', 1 => '2'],
         darray[0 => 's3', 'digit' => '3', 1 => '3'],
-        darray[0 => 't', 'digit' => '', 1 => ''],
+        darray[0 => 't'],
       ]),
       tuple('test', re"/a/", 0, vec[]),
       tuple('t1e2s3t', re"/[a-z]/", 3, vec[