Remove .NET Framework remarks (System.Security.Policy)

[gewarren]

.NET Framework API ref has moved to its own repo (https://github.com/dotnet/dotnetfw-api-docs), so we can clean up .NET Framework remarks, exceptions, and code examples out of this repo. Contributes to #12513.

Removes remarks and examples related to:

• .NET Framework versions
• Code-access security
• Configuring apps via app.config file
• App domains

Also removes all remarks from obsolete APIs.

Hide whitespace changes

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/area-system-security, @vcsjones

[Copilot]

Pull request overview

This PR cleans up the System.Security.Policy API reference XML in this repo by removing .NET Framework-specific remarks, examples, and other legacy guidance now that .NET Framework API docs have moved to a separate repository.

Changes:

• Removed CAS/.NET Framework-era explanatory remarks and external links (for example, CASPOL/SN/App.config/AppDomain guidance) from multiple System.Security.Policy types.
• Removed some member-level remarks/examples blocks (including snippet includes) and simplified remaining remarks sections.
• Updated a few remarks blocks for formatting/wording consistency.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 46 comments.

Show a summary per file

File	Description
xml/System.Security.Policy/Zone.xml	Removes legacy CAS/zone-mapping remarks from type/members.
xml/System.Security.Policy/Url.xml	Removes legacy CAS URL evidence remarks content.
xml/System.Security.Policy/UnionCodeGroup.xml	Removes CAS policy remarks and examples from members.
xml/System.Security.Policy/StrongNameMembershipCondition.xml	Removes strong-name/CAS remarks content from members.
xml/System.Security.Policy/StrongName.xml	Removes strong-name/CAS remarks content and legacy links.
xml/System.Security.Policy/Site.xml	Removes legacy CAS site evidence remarks content.
xml/System.Security.Policy/PublisherMembershipCondition.xml	Removes Authenticode/CAS remarks content.
xml/System.Security.Policy/Publisher.xml	Removes legacy CAS publisher evidence remarks content.
xml/System.Security.Policy/PolicyLevel.xml	Removes CLR security policy remarks/examples and some related references.
xml/System.Security.Policy/PermissionRequestEvidence.xml	Removes legacy policy-system remarks and member remarks blocks.
xml/System.Security.Policy/NetCodeGroup.xml	Removes extensive CAS policy remarks/examples describing connection rules.
xml/System.Security.Policy/IIdentityPermissionFactory.xml	Removes legacy CAS demand/identity-permission explanation text.
xml/System.Security.Policy/GacInstalled.xml	Removes legacy CAS GAC identity remarks from members.
xml/System.Security.Policy/FirstMatchCodeGroup.xml	Removes CAS policy remarks describing evaluation semantics.
xml/System.Security.Policy/FileCodeGroup.xml	Removes CAS policy remarks describing file permission semantics.
xml/System.Security.Policy/EvidenceBase.xml	Trims .NET Framework version history and rewrites remarks content.
xml/System.Security.Policy/CodeGroup.xml	Removes CAS policy remarks/examples across many members.
xml/System.Security.Policy/ApplicationTrust.xml	Removes sandbox/AppDomain-related remarks content.
xml/System.Security.Policy/ApplicationDirectory.xml	Converts type-level remarks to a shorter inline form and normalizes markdown blocks.