Addresses: filesys.ts

Use of the term a 'non-privileged' process. The comment for available in the struct space_info refers to: free space available to a non-privileged process. This seems quite specific to a POSIX implementation (on Windows, for instance, the equivalent data would be user-specific but not directly related to privilege)

Remove the comment and add a note to 15.32 [fs.op.space]: [Note: the precise meaning of available space is implementation dependent. — end note]