Revert "Revert "Remove legacy-test and legacy-android-test targets""

Fixes up the android.test.legacy target to stop using sources directly
now that the issue with android.test.runner-minus-junit not being able
to be built against the SDK has been resolved.

Also, fixes a couple of comments.

This reverts commit 7d7af10dc9057a49c617c7c97c174e8b4ec5008c.

Reason for revert: When this was originally applied it broke the
pi-dev-plus-aosp branch as it contained references to these targets.
Those references have now been removed.

Bug: 63127064
Change-Id: I619e92faf4cc38f8fd4f053bde832e9a76a2a2bf
Test: make checkbuild
diff --git a/test-runner/Android.bp b/test-runner/Android.bp
index db5053e..3521202 100644
--- a/test-runner/Android.bp
+++ b/test-runner/Android.bp
@@ -45,7 +45,7 @@
 
 // Build the android.test.runner-minus-junit library
 // =================================================
-// This is only intended for inclusion in the legacy-android-test static
+// This is only intended for inclusion in the android.test.legacy static
 // library and must not be used elsewhere.
 java_library {
     name: "android.test.runner-minus-junit",