Remove outdated prompt for creating pull requests for Preview 7

Author: jamesmontemagno

.github/prompts/createprs-for-preview.prompt.md

@@ -1,27 +0,0 @@
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-mode: agent
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-Go through each folder in release-notes/10.0/preview7 and one at a time i want you do to the following:
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-1. create a new branch names **dotnet10-p7-<name>** where <name> is the name of the file without the extension.
-2. modify the file in some simple way by adding a new line at the end of the file with the text "Something about the feature" in it.
-3. commit the change with the message "Update <name> for preview 7" where <name> is the name of the file without the extension.
-4. push the branch to the remote repository.
-5. create a pull request with the title "Update <name> for preview 7" and the body "This PR updates the <name> file for preview 7. Please make any additional changes to this based on the new items." where <name> is the name of the file without the extension.
-6. go back to the dotnet10-p7 branch and repeat the process for the next file.
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-Here are the files you need to do this one at a time for:
-- aspnetcore.md
-- containers.md
-- csharp.md
-- dotnetmaui.md
-- efcore.md
-- fsharp.md
-- libraries.md
-- runtime.md
-- sdk.md
-- visualbasic.md
-- winforms.md
-- wpf.md