PROTON-2201, PROTON-2154: drop version back to 0.31.0-SNAPSHOT

This reverts commits c2384ecdc7b7490fa2ed95fc121d8188122661e3 and b6532632d6b0877136621daeba55b2e105d810d2.
diff --git a/VERSION.txt b/VERSION.txt
index fcc99b1..df48e23 100644
--- a/VERSION.txt
+++ b/VERSION.txt
@@ -1 +1 @@
-0.32.0-SNAPSHOT
+0.31.0-SNAPSHOT