Install recovery etc files to recovery/root/system/etc.

They used to be installed under recovery/root/etc. This CL moves the
files to the new location and creates a symlink from /etc to /system/etc
(done by the rule in system/core/rootdir). This gives similar layout
between normal boot and recovery, and allows installing prebuilt_etc
files with Soong (`recovery_available: true`).

As part of the change, we no longer need the whitelisting rule for
mke2fs.conf.

Bug: 112780007
Test: Build with other changes in the topic (aosp_taimen-userdebug).
      Check the generated files under recovery (/etc being a symlink to
      /system/etc).
Test: Boot into recovery. Verify basic functionalities (`adb shell` and
      `adb sideload`, factory reset).
Test: `build/soong/build_test.bash --dist`
Change-Id: Ibb6dea6f179a339f0c2d0fd8ba05ec0085b79a12
diff --git a/CleanSpec.mk b/CleanSpec.mk
index 903f0c9..398a006 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -500,6 +500,9 @@
 $(call add-clean-step, find $(PRODUCT_OUT) -type d -name "*product-services*" -print0 | xargs -0 rm -rf)
 $(call add-clean-step, find $(PRODUCT_OUT) -type l -name "*product-services*" -print0 | xargs -0 rm -rf)
 
+# Remove obsolete recovery etc files
+$(call add-clean-step, rm -rf $(TARGET_RECOVERY_ROOT_OUT)/etc)
+
 # ************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************