remove parenthetical information from field name
remove parenthetical information from field name

Note: This may or may not be a correction. "Seasonally corrected" is clearly a subhead for the Trend column in the [archived file]. However, the note in the file says, "We then determine the 'trend' value for each month by removing the seasonal cycle."

[archived file]: https://raw.githubusercontent.com/datasets/co2-ppm/master/archive/co2_mm_mlo.txt
datasets/co2-ppm