Remove dead code

Remove dead code

There is a perhaps-surprisingly large amount of code disabled behind
directives like '#if 0', '#ifdef notdef', and '#ifdef notyet'. At
best, this code is clutter, and at worst some of it is
confusing/outdated, and/or confusingly nested inside other
preprocessor conditionals. Sometimes this disabled code shows up when
grepping the tree, and causes a nuisance when refactoring related
areas of code.

Get rid of all of it. If anyone ever wants this code back, it can
always be restored by reverting portions of this commit.

Also delete some comments that clearly refer to the disabled code, and
in some cases, adjust the adjacent comments to make sense accordingly.

This commit doesn't touch any files in src/external/.

Change-Id: If260a41257e8d107930bd3c177eddb8ab336f0d1
Reviewed-on: https://gerrit.openafs.org/13683
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: Benjamin Kaduk <kaduk@mit.edu>