Revert of DEPS: Update leveldatabase from 1.18 to 1.20.

third_party/leveldatabase/BUILD.gn

Index: third_party/leveldatabase/BUILD.gn
diff --git a/third_party/leveldatabase/BUILD.gn b/third_party/leveldatabase/BUILD.gn
index d943efac02792bb281e89064bf86ff8c925d337b..c8776c887c38929d645fd2f02a0c0879738f72c6 100644
--- a/third_party/leveldatabase/BUILD.gn
+++ b/third_party/leveldatabase/BUILD.gn
@@ -12,21 +12,6 @@
     "src",
     "src/include",
   ]
-}
-
-source_set("leveldatabase_opts.sse42") {
-  sources = [
-    "src/port/port_posix_sse.cc",
-  ]
-
-  configs += [ ":leveldatabase_config" ]
-
-  if (target_cpu == "x86" || target_cpu == "x64") {
-    defines += [ "LEVELDB_PLATFORM_POSIX_SSE" ]
-    if (!is_win || is_clang) {
-      cflags = [ "-msse4.2" ]
-    }
-  }
 }
 
 static_library("leveldatabase") {
@@ -123,7 +108,6 @@
   public_configs = [ ":leveldatabase_config" ]
 
   deps = [
-    ":leveldatabase_opts.sse42",
     "//base",
     "//base/third_party/dynamic_annotations",
     "//third_party/re2",