Replace <rpc/types.h> with <rx/xdr.h>

Replace <rpc/types.h> with <rx/xdr.h>

Our in-tree xdr.h appears to have started life as a concatenation of
rpc/types.h and rpc/xdr.h, and should include all the needed functionality.
Indeed, commit 7293ddf325b149cae60d3abe7199d08f196bd2b9 even indicates
that we expect to be using our in-tree XDR everywhere anyway, so the
system XDR is superfluous.

Note that afs/sysincludes.h (not afsincludes.h!) already includes
rx/xdr.h ifndef AFS_LINUX22_ENV.

This change should help systems running glibc 2.26 or newer, which has
stopped providing the Sun RPC headers by default.

While here remove some duplicate includes of rpc/types.h in the
AIX-specific sources.

The Solaris NFS translator bits cannot really be changed, since the system
headers are used and have tight interdependencies.

Update rxgen to not emit rpc/types.h inclusion.

[mmeffie: squash 12801 to not emit rpc/types.h from rxgen]

Change-Id: I0b195216affa06ab9e259cb0bab0c8286a1636d9
Reviewed-on: https://gerrit.openafs.org/12800
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>