Update UltraSonicSensors.java

Changes done by Erik, after Vic got the sensors to work. This code has not yet been tested.
Summary of changes:
1) Now that the PulseInput are opened and closed within the read() method, there is no need for corresponding instance variables. Removed leftInput, frontInput, and rightInput
2) Corrected spelling of righttStrobe to rightStrobe
3) Closing rightStrobe and frontStrobe in closeConnection()
4) Minor other changes; see diff