Revert "Change DISCLAIMER to DISCLAIMER-WIP (#6442)" (#8845)

This reverts commit 7bf1be2.

Author: yaooqinn

DISCLAIMER

@@ -0,0 +1,10 @@
+Apache Gluten (Incubating) is an effort undergoing incubation at the Apache
+Software Foundation (ASF), sponsored by the Apache Incubator PMC.
+
+Incubation is required of all newly accepted projects until a further review
+indicates that the infrastructure, communications, and decision making process
+have stabilized in a manner consistent with other successful ASF projects.
+
+While incubation status is not necessarily a reflection of the completeness
+or stability of the code, it does indicate that the project has yet to be
+fully endorsed by the ASF.