Switch 1 of 2 Windows ASan builder to 64-bit.

R=dpranke@chromium.org

Bug: 783296
Change-Id: Id7331db499a8e448c8e58cabab4e7b170e45db93
Reviewed-on: https://chromium-review.googlesource.com/821853
Commit-Queue: Abhishek Arya <inferno@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523515}

tools/mb/mb_config.pyl

@@ -358,7 +358,7 @@
       'UBSan Release': 'ubsan_release_bot',
       'UBSan vptr Release': 'ubsan_vptr_edge_release_bot',
       'Win ASan Release Media': 'asan_fuzzer_v8_heap_chrome_with_codecs_release_bot_x86',
-      'Win ASan Release': 'asan_fuzzer_v8_heap_release_bot_x86',
+      'Win ASan Release': 'asan_fuzzer_v8_heap_release_bot',
       'Win SyzyASAN LKGR': 'syzyasan_no_pch_release_x86',
     },
 
@@ -1045,8 +1045,8 @@
       'clang', 'asan', 'fuzzer', 'v8_heap', 'chrome_with_codecs', 'release_bot', 'x86',
     ],
 
-    'asan_fuzzer_v8_heap_release_bot_x86': [
-      'clang', 'asan', 'fuzzer', 'v8_heap', 'release_bot', 'x86',
+    'asan_fuzzer_v8_heap_release_bot': [
+      'clang', 'asan', 'fuzzer', 'v8_heap', 'release_bot',
     ],
 
     'asan_lsan_chromeos_release_trybot': [