cleanup: unused ifdef'd code in IPPL
The following macros are never set or used:

IPPL_COMM_ALARMS
see #412 (closed) 
IPPL_GDL
see #413 (closed) 
IPPL_DIRECTIO
see #414 (closed) 
IPPL_IOFLAG_BUG
see #415 (closed) 
IPPL_MPIXX
see #416 (closed) 
IPPL_NETCDF
see #417 (closed) 
IPPL_PM
se #421 (closed) 
IPPL_PRINTDEBUG
see #422 (closed) 
IPPL_PURIFY
see #424 (closed) 
IPPL_RUNTIME_ERRCHECK
see #419 (closed) 
IPPL_SGI_PRAGMAS
see #427 (closed) 
IPPL_SHMEMPI
see #421 (closed) 
IPPL_TFLOP
see #428 (closed) 
IPPL_USE_PARTIAL_SPECIALIZATION
(if not defined) see #430 (closed) 
IPPL_USE_FUNKY_VEC_COPIES
see #431 (closed) 
IPPL_USE_MEMBER_TEMPLATES
see #443 (closed) 
IPPL_USE_STANDARD_HEADERS
see #440 (closed) 
IPPL_USE_RAND_RNG
see #441 (closed) 
IPPL_USE_SIMPLE_RNG
see #441 (closed) 
IPPL_USE_XCI_RNG
see #441 (closed) 
IPPL_USE_SINGLE_PRECISION
see #437 (closed) 
IPPL_XT3
see #436 (closed) 
OLD_IPPL_PGI
see #434 (closed) 
SGI_TIMERS
see #428 (closed) 
TULIP_TIMERS
see #428 (closed) 
__MWERKS__
see #429 (closed) 
HAVE_EXPDE
(and subsequently ParticleLayoutFromGrid.h) see #444 (closed) 
IPPL_DKS_MIC
see #445 (closed) 
OLD_SWAP_PARTICLES
see #446 (closed) 
UNDEFINED
see #448 (closed)
What can be removed? @snuverink_j @frey_m @kraus @adelmann : please check what can be removed!
All ticked will be removed!