[tests] Remove now unused co19_2 directory

Seems it was accidentally added back in a recent CL.

Change-Id: I21463c64a6c0169234beacfbe2c86ed327a88036
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/339501
Auto-Submit: Parker Lougheed <parlough@gmail.com>
Reviewed-by: Erik Ernst <eernst@google.com>
Reviewed-by: Alexander Thomas <athom@google.com>
diff --git a/tests/co19_2/src b/tests/co19_2/src
deleted file mode 160000
index 0454b17..0000000
--- a/tests/co19_2/src
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 0454b178fdf6697e898b5e5c7ee553a9bc266faa