Revert "Fixes #3674: change the index to index node, execution timestamp"

This reverts commit 40ed6ddbee92b6a42eaf667b8077b10005c85f84.
Fixes #3674: add composite index to improve perfs on node list page
Merge pull request #314 from ncharles/bug_3674/dev/change_index_on_reports

Bug 3674/dev/change index on reports
Merge branch 'branches/rudder/2.6' into branches/rudder/2.7