[logging] Remove backend_legacy

Executables include the proper backend handling both host and fuchsia.

Bug: 101561

Change-Id: I2d318468408537eab87170c0dac2355b70e85afa
diff --git a/BUILD.gn b/BUILD.gn
index 85353d9..11986cd 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -95,7 +95,6 @@
 
   deps = [
     ":qjs-lib",
-    "//sdk/lib/syslog/cpp:backend_legacy",
     "//src/lib/fxl/test:gtest_main",
     "//third_party/googletest:gtest",
   ]