Respond to PR code review comments for ported library System.Security.AccessControl

[venkat-raman251]

@GiriSr as the owner of the System.Security.AcessControl library can you please have a look through the code review comments provided in dotnet/corefx#4977 and address them appropriately.

[venkat-raman251]

Please address/remove the TODO's in the code.

[venkat-raman251]

@weshaggard : Who is the owner of this library to assign this issue to? And is this for rc2?

[weshaggard]

@GiriSr is the owner and I don't think this is needed for RC2 it is just clean-up.

[venkat-raman251]

@weshaggard : @GiriSr hasn't been active on github from what i can see. That was the reason this was assigned back to me.

[Clockwork-Muse]

Additionally, there appears to be no .sln file, and no tests.

[niemyjski]

What's the status of this?