Updating IsControl Char page

[IndigoShock]

Summary

The goal is to make this page more concise and readable

• Deleted an extraneous T in the third Remarks section.
• Deleted the Remarks section at the top because under each example has their own Remarks section.

Fixes #Issue_Number (if available)

[rpetrusha]

Thank you, @IndigoShock, for contributing to the dotnet/dotnet-api-docs repo and elmininating duplication on this page. I thought, though, that a better option is to leave the paragraph in the Remarks section at the top of the page and remove it for the individual method overloads.

[rpetrusha]

Thanks both for contributing to making the documentation more concise, @IndigoShock. I'll merge your PR now.