nice: remove useless translations

Author: sylvestre

src/uu/nice/locales/en-US.ftl

@@ -4,11 +4,9 @@ nice-about = Run COMMAND with an adjusted niceness, which affects process schedu
 nice-usage = nice [OPTION] [COMMAND [ARG]...]
 
 # Error messages
-nice-error-getpriority = getpriority: { $error }
 nice-error-command-required-with-adjustment = A command must be given with an adjustment.
 nice-error-invalid-number = "{ $value }" is not a valid number: { $error }
 nice-warning-setpriority = { $util_name }: warning: setpriority: { $error }
-nice-error-execvp = execvp: { $error }
 
 # Help text for command-line arguments
 nice-help-adjustment = add N to the niceness (default is 10)