Remove an obsolete TODO

* Xcode's Swift 2.3 toolchain was an artifact
of the Swift migration period and doesn't seem
to be present in newer versions. Spending time
on a likely unused feature isn't worth the time
anymore.

PiperOrigin-RevId: 166851949

tools/build_defs/apple/swift.bzl

diff --git a/tools/build_defs/apple/swift.bzl b/tools/build_defs/apple/swift.bzl
index 656496e..a8f1a16 100644
--- a/tools/build_defs/apple/swift.bzl
+++ b/tools/build_defs/apple/swift.bzl
@@ -112,7 +112,6 @@
 
     # We cannot use non Xcode-packaged toolchains, and the only one non-default
     # toolchain known to exist (as of Xcode 8.1) is this one.
-    # TODO(b/29338444): Write an integration test when Xcode 8 is available.
     if toolchain == "com.apple.dt.toolchain.Swift_2_3":
       toolchain_name = "Swift_2.3"