Use re2_fuzzer stored in re2 repository, remove old version.

third_party/re2/BUILD.gn

Index: third_party/re2/BUILD.gn
diff --git a/third_party/re2/BUILD.gn b/third_party/re2/BUILD.gn
index 4ced4b2f15b44455825ee0cd38ddf6d61b01eac6..b96f75402bfbb70742216b4dfcbcd593ee5226da 100644
--- a/third_party/re2/BUILD.gn
+++ b/third_party/re2/BUILD.gn
@@ -2,6 +2,8 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//testing/libfuzzer/fuzzer_test.gni")
+
 config("re2_config") {
   include_dirs = [ "src" ]
 }
@@ -57,3 +59,12 @@ static_library("re2") {
   configs += [ "//build/config/compiler:no_chromium_code" ]
   public_configs = [ ":re2_config" ]
 }
+
+fuzzer_test("third_party_re2_fuzzer") {
+  sources = [
+    "src/re2/fuzzing/re2_fuzzer.cc",
+  ]
+  deps = [
+    ":re2",
+  ]
+}