[sdk][bazel] Remove safeguard for the main package's dilp file.

The kernel compiler used to not generate a dilp file for the main
package, instead generating a %{name}_kernel.dil-main.dilp file.
Declaring that file used to throw bazel errors as it wasn't generated.
This safeguard is no longer necessary as the dilp files generation is
wrapped under a script file that checks for existence and emptiness and
is safe to remove.

Bug: DX-851
Test: all tests pass, example dart_app run on target.
Change-Id: I48184a5ec1774c4e1125fdae7d63411fdcc63d09
diff --git a/sdk/bazel/base/dart/build_defs/dart.bzl b/sdk/bazel/base/dart/build_defs/dart.bzl
index 5b84692..00e9117 100644
--- a/sdk/bazel/base/dart/build_defs/dart.bzl
+++ b/sdk/bazel/base/dart/build_defs/dart.bzl
@@ -100,10 +100,6 @@
     mappings = {}
     dart_ctxs = collect_dart_context(dart_ctx).values()
     for dc in dart_ctxs:
-        # There's no need to declare a file for the current package as it
-        # is outputed under `main_dilp_file`.
-        if dc.package == package_name:
-            continue
         dilp_file = context.actions.declare_file(
             context.label.name + "_kernel.dil-" + dc.package + ".dilp",
         )