Remove afsio warnings and errors

Remove afsio warnings and errors

Fix a few warnings and errors in afsio, so it can compile:

 - inlcude rx/rx_prototypes.h, not rx_prototypes.h

 - only declare 'code' in SRXAFSCB_TellMeAboutYourself, and the global
   rx_mtu in AFS_NT40_ENV, since they're only used on NT40

 - remove declarations of the unused variables 'host' in
   HandleLocalAuth, 'i' in readFile, and 'i' in writeFile

Change-Id: If39420cca791669200ccb4d3f46aa5ac7eb89c7d
Reviewed-on: http://gerrit.openafs.org/2121
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>