Remove TODO comment about producing native components for test only

According to
<https://docs.gradle.org/current/userguide/native_software.html>,
"When you assemble dependents of a component, the component and all of
its dependents are compiled and linked, including any test suite
binaries."  So it's intentional that the "assemble" task causes
creation of the smoke_main executable and xlator_test shared library.
Nothing TODO here; the current behavior is as designed.

com.ibm.wala.cast.test/build.gradle

@@ -18,8 +18,6 @@ dependencies {
 		)
 }
 
-// TODO: build following targets for "test"-only, not "main"
-
 def currentJvm = org.gradle.internal.jvm.Jvm.current()
 
 task generateJniHeaders(type: Exec, dependsOn: [testClasses, ':com.ibm.wala.cast:classes']) {