Revert the addition of tooltips to most SecureQLabel occurrences

[rmol]

Description

Tooltips are only needed in the conversation view for long filenames that get truncated.

Fixes #1015.

Test Plan

Start the client. Confirm that tooltips are not shown for the preview snippets in the source list, or any content in the conversation view except for long filenames that need to be truncated. You'll need to upload a document with a long filename to test that.

Checklist

If these changes modify code paths involving cryptography, the opening of files in VMs or network (via the RPC service) traffic, Qubes testing in the staging environment is required. For fine tuning of the graphical user interface, testing in any environment in Qubes is required. Please check as applicable:

• I have tested these changes in the appropriate Qubes environment
• I do not have an appropriate Qubes OS workstation set up (the reviewer will need to test these changes)
• These changes should not need testing in Qubes

If these changes add or remove files other than client code, packaging logic (e.g., the AppArmor profile) may need to be updated. Please check as applicable:

• I have submitted a separate PR to the packaging repo
• No update to the packaging logic (e.g., AppArmor profile) is required for these changes
• I don't know and would appreciate guidance

[sssoleileraaa]

lgtm (tested and fixes the issue)