Revert "Default to Server level context for all OE nodes (#829)"

[Charles-Gagnon]

Fixes microsoft/azuredatastudio#6497 microsoft/azuredatastudio#6394

This reverts commit a4b6c30. Two reasons for reverting this :

1. There's been numerous complaints (Connections on connections panel now go to server root instead of selected database azuredatastudio#6394) about the change in behavior
2. It broke Data Explorer nodes and while the long term "best" fix may be to have a single connection per node and then have child nodes update their context appropriately - but this is going to require more investigation and time to implement correctly so doing this lets us fix the completely broken experience until that can be done correctly

[coveralls]

Coverage increased (+4.9%) to 76.433% when pulling 6898868 on chgagnon/revertConnectionContext into f7a7a3d on master.

[Charles-Gagnon]

@kburtram @kevcunnane I'm planning on merging this in today unless either of you have any issue with this