trivial: Remove 'tools/releasenotes_tox.sh'

This is not needed since reno 2.1.0 (commit f8fc8f97) [1].

[1] https://github.com/openstack/reno/commit/f8fc8f97ff20026582742e3e7838cdd0ed5cad68

Change-Id: I66ba0e0835970b965acce00ba69d143bd4471037

tools/releasenotes_tox.sh

@@ -1,28 +0,0 @@
-#!/usr/bin/env bash
-
-rm -rf releasenotes/build
-
-sphinx-build -a -E -W \
-    -d releasenotes/build/doctrees \
-    -b html \
-    releasenotes/source releasenotes/build/html
-BUILD_RESULT=$?
-
-UNCOMMITTED_NOTES=$(git status --porcelain | \
-    awk '$1 ~ "M|A|??" && $2 ~ /releasenotes\/notes/ {print $2}')
-
-if [ "${UNCOMMITTED_NOTES}" ]
-then
-    cat <<EOF
-
-REMINDER: The following changes to release notes have not been committed:
-
-${UNCOMMITTED_NOTES}
-
-While that may be intentional, keep in mind that release notes are built from
-committed changes, not the working directory.
-
-EOF
-fi
-
-exit ${BUILD_RESULT}