Revert "Disable user poisoning in swift LLDB"

This reverts commit 720c769.

Author: adrian-prantl

lldb/test/Unit/lit.cfg.py

@@ -43,12 +43,6 @@
 # false positive in std::vector. We also want to support testing a sanitized
 # lldb using unsanitized llvm, clang, and swift libraries.
 config.environment['ASAN_OPTIONS'] += ':' + 'detect_container_overflow=0'
-
-# FIXME: This is the wrong place to disable this. This is working
-# around the fact that the ci.swift.org scripts build only LLDB with
-# asan and this creates an ODR violation in Allocator.h that breaks
-# poisoning.
-config.environment['ASAN_OPTIONS'] += ':' + 'allow_user_poisoning=0'
 # End Swift mod.