Move mode switch from the interface part of the unit to the area betw…

[JPeterMugaas]

…een the "unit" and "interface" for good measure

[JPeterMugaas]

I moved the IdCompilerDefines.inc to between the "unit" and "imterface" declarations because of this:

From the Free Pascal Conversion Guide:
https://wiki.lazarus.freepascal.org/Code_Conversion_Guide

Most Delphi units can be compiled by the Free Pascal compiler by adding:

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}

right after the unit name.

[rlebeau]

Where the IdCompilerDefines.inc references are located right now is fine, they have worked fine for years without problem. They don't need to be moved:

https://www.freepascal.org/docs-html/user/userse33.html

The MODE directive should always be located before the uses clause of the unit interface or program uses clause, because setting the mode may result in the loading of an additional unit as the first unit to be loaded.

Moving the .inc references above the interface block doesn't offer any real benefit, only minor code cleanup. I'm already doing some other code cleanups in Indy 11, so I would defer such a big change until then.

But, removing unused unit references is good. I have incorporated those changes now.