cleaning: no useless color definition

* no color definition in PS1 setting, if the functionnalitie is desactivated there is no need to define a color
* no NO_COL in the begining of functionnalitie output, the previous one is supposed to end with a clean color (NO_COL)
do not recalculate darwin kernel version at each prompt set
it doesn't seem that LP_USER need to be defined at each prompt set