Don't depend on Dart from FML. (#162271)

This was likely a holdover from a time when trace events were routed to
the timeline directly.

This was causing standalone QNX builds to also pull in Dart.

No change in functionality and hopefully faster builds for smaller
targets.

engine/src/flutter/fml/BUILD.gn

@@ -113,12 +113,7 @@ source_set("fml") {
     ":string_conversion",
   ]
 
-  deps = [
-    "$dart_src/runtime:dart_api",
-
-    # These need to be in sync with the Fuchsia buildroot.
-    "//flutter/third_party/icu",
-  ]
+  deps = [ "//flutter/third_party/icu" ]
 
   if (enable_backtrace) {
     # This abseil dependency is only used by backtrace.cc.