Removed redundant preprocessor directives
Removed redundant preprocessor directives

In the newer versions of the IDE it is sufficient to simply include
the Arduino.h header file.

Fixes #463

AnalysIR/Arduino-IRremote,shirriff/Arduino-IRremote,z3t0/Arduino-IRremote,Seeed-Studio/IRSendRev,z3t0/Arduino-IRremote,shirriff/Arduino-IRremote,Seeed-Studio/IRSendRev,AnalysIR/Arduino-IRremote