CMakeLists.txt: Don't set MARL_BUILD_TESTS to OFF

This is now the default in marl.

Bug: b/140546382
Change-Id: Ic28537760b38c9ee051c8e527791495a57117466
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36190
Tested-by: Ben Clayton <bclayton@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9fc93a5..924887d 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -2009,7 +2009,6 @@
 endif()
 
 if(BUILD_MARL)
-    set(MARL_BUILD_TESTS OFF)
     add_subdirectory(third_party/marl)
 endif(BUILD_MARL)