[CMake] Don't explicitly set folder for InstrumentationTests (#170041)

Use the default of `LLVM/Tests/Unit` to group these tests with other
LLVM unit test targets in the IDE.

llvm/unittests/Transforms/Instrumentation/CMakeLists.txt

diff --git a/llvm/unittests/Transforms/Instrumentation/CMakeLists.txt b/llvm/unittests/Transforms/Instrumentation/CMakeLists.txt
index 78a1314..9ce3ab4 100644
--- a/llvm/unittests/Transforms/Instrumentation/CMakeLists.txt
+++ b/llvm/unittests/Transforms/Instrumentation/CMakeLists.txt
@@ -14,5 +14,3 @@
   )
 
 target_link_libraries(InstrumentationTests PRIVATE LLVMTestingSupport)
-
-set_property(TARGET InstrumentationTests PROPERTY FOLDER "Tests/UnitTests/TransformTests")