Revert of Update FlatBuffers to include multiple improvements. (patchset #5 id:80001 of https://codereview.chromium.org/2883063002/ )

Reason for revert:
Fails "Win" build: https://build.chromium.org/p/chromium/builders/Win/builds/55836

Original issue's description:
> Update FlatBuffers to include multiple improvements.
>
> This CL updates FlatBuffers to the latest version 1.6.x. This is necessary to
> include the following changes to the library:
>  - d7ac378: Offset<T>::IsNull method.
>  - 93c0960: --keep-prefix compiler option.
>  - c559eb4: Generate files for empty schemas.
>  - aaf5598: Fix path comparison on Windows.
>  - fb87c0d: Improve allocator handling (fixes test).
>  - 22743ca: Fix --keep-prefix bugs.
>  - 642254b: Fix one more --keep-prefix issue.
>  - dd05f32: Add tests for nested FlatBuffers.
>  - 01c50d5: Get rid of move semantics in VectorIterator.
>
> BUG=611351,713774
>
> Review-Url: https://codereview.chromium.org/2883063002
> Cr-Commit-Position: refs/heads/master@{#477254}
> Committed: https://chromium.googlesource.com/chromium/src/+/387b2a94017449569f0f5b2f865d3331e3646a3a

[email protected],[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=611351,713774

Review-Url: https://codereview.chromium.org/2926563002
Cr-Commit-Position: refs/heads/master@{#477258}
diff --git a/DEPS b/DEPS
index 9d77a07..282bad33 100644
--- a/DEPS
+++ b/DEPS
@@ -223,7 +223,7 @@
     Var('chromium_git') + '/chromium/deps/flac.git' + '@' + '7d0f5b3a173ffe98db08057d1f52b7787569e0a6',
 
   'src/third_party/flatbuffers/src':
-    Var('chromium_git') + '/external/github.com/google/flatbuffers.git' + '@' + '01c50d57a67a52ee3cddd81b54d4647e9123a290',
+    Var('chromium_git') + '/external/github.com/google/flatbuffers.git' + '@' + 'e92ae5199d52fd59540a800bec7eef46cd778257',
 
   'src/third_party/pyftpdlib/src':
     Var('chromium_git') + '/external/pyftpdlib.git' + '@' + '2be6d65e31c7ee6320d059f581f05ae8d89d7e45',