Removed redundant sanity check

Removed useless and redundant sanity check on the Pin number, because the `command.startsWith("A0")` portion of the code takes care of it.
Possible improvement : allow to attach new servos at runtime, with another Spark function call, then handle pin number in the `servowrite` function.
Merge pull request #4 from Hexalyse/patch-1

Removed redundant sanity check