Remove err_occurred function and commented code.

All the parameter reading subroutines report errors through an argument,
so this function does nothing. The variable it returns is never assigned
the errors anyway.
Remove unnecessary string trimming.

These strings are trimmed when extracted from the Par_file, so there's
no need to do it again. What's worse in this case is the string is
trimmed in a loop over all receivers.
Remove Par_file variable prefixes.

These are not used by the Par_file parsing code. Some places even didn't
have them.