Remove stray backtick in "MFC Classes" title and some cleanups

[Rageking8]

• Remove stray backtick in "MFC Classes" title and some metadata cleanups
• Replace br elements with escapes (replace all <br/> with \)
• Simplify relative links (replace all ../../mfc/reference/ with nothing, then replace all ../../mfc/ with ../)
• Fix unmatched backtick for CMFCTabToolTipInfo structure link
• Fix unmatched parenthesis for CMFCDropDownToolBar class link

Best reviewed one commit at a time.

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Learn Build status updates of commit a67cdc9:

✅ Validation status: passed

File	Status	Preview URL	Details
docs/mfc/reference/mfc-classes.md	✅Succeeded

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PRMerger Results

Issue	Description
File Change Percent	This PR contains file(s) with more than 30% file change.

[v-regandowner]

@TylerMSFT - Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
@MicrosoftDocs/public-repo-pr-review-team

[TylerMSFT]

Thank you for fixing that--particularly the backtick in the title.
After looking at the diff, I suppose you have a new appreciation for search and replace ;-)

[TylerMSFT]

#sign-off