Linux: remove some 2.6 specific code from 2.4

Linux: remove some 2.6 specific code from 2.4

Remove some code that will never be compiled or used in the
afs/LINUX24 directory.
This includes code depending on AFS_LINUX26_ENV, and on
LINUX_USE_FH which is never set in 2.4 and is going away
soon anyway.

Change-Id: I972262b45d3518d996756b5dc9f6e6c01450e5cc
Reviewed-on: http://gerrit.openafs.org/2259
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>