Revert "Show reasons for regenerating the ninja file"

This reverts commit 027cf0aa484b7602f4a653d1e6e287ce02d3d44a.

Reason for revert: It may need more discussion about set the flag by default, revert it first.

Change-Id: I42f9a449b69b54ce5d906e12c7f611107e219894
diff --git a/atest/atest_main.py b/atest/atest_main.py
index 3609f89..b3409e1 100755
--- a/atest/atest_main.py
+++ b/atest/atest_main.py
@@ -946,8 +946,6 @@
     # Changing this variable does not retrigger builds.
     atest_utils.update_build_env(
         {'ANDROID_QUIET_BUILD': 'true',
-         #(b/271654778) Showing the reasons for the ninja file was regenerated.
-         'SOONG_UI_NINJA_ARGS': '-d explain',
          'BUILD_OUTPUT_MODE': mode.value})