Originally Posted by FBinNY

Unless there's an issue of chainring selection, you can simply remove the third chainring. Ideally you'd want to move the crank inboard by about 3mm to correct the chainline difference (assumes it was right in the first place), but in many cases it isn't necessary.

If you do replace the crank, you may or may not need to replace the bottom bracket or spindle depending on what the new crank calls for.