Disable FutureReturnValueIgnored error prone check

Turns out this has a bug, so we turn it off until it's fixed.
This problem can be reproduced in this change (ps9):
https://gerrit-review.googlesource.com/c/gerrit/+/317099/9

Change-Id: Ie064485e06388bf80e66e0cf850263a469b72c27
diff --git a/tools/BUILD b/tools/BUILD
index 1bace53..64b0665 100644
--- a/tools/BUILD
+++ b/tools/BUILD
@@ -202,7 +202,7 @@
         "-Xep:FromTemporalAccessor:ERROR",
         "-Xep:FunctionalInterfaceClash:ERROR",
         "-Xep:FunctionalInterfaceMethodChanged:ERROR",
-        "-Xep:FutureReturnValueIgnored:ERROR",
+        # "-Xep:FutureReturnValueIgnored:ERROR", // this check has a bug.
         "-Xep:FuturesGetCheckedIllegalExceptionType:ERROR",
         "-Xep:GetClassOnAnnotation:ERROR",
         "-Xep:GetClassOnClass:ERROR",