Strip some security related attributes (#8571)

Strip some security related attributes (#8571)

Strips SecurityCritical, SecuritySafeCritical, SecurityPermission,
EnvironmentPermission, and PermissionSet attributes.

Also removes empty defines these left behind.

Patterns used:

^.*\[(System\.Security\.)?SecurityCritical\](\s*//.*|\s*)$[\r\n]*
^.*#if FEATURE_CORECLR[\s\r\n]*(#else)?[\s\r\n]*#endif.*[\r\n]*
^.*\[(System\.Security\.Permissions\.)?SecurityPermission(Attribute)?\([^)]*\)\](\s*//.*|\s*)$[\r\n]*