Fix donate bug, remove donate junk chance

Remove the chance of a donated object getting junked instead.
This also fixes issue #325.
When donating an object, sometimes the object would remain in the character's inventory. This was specifically due to a call to extract_obj() near the end of the file which used a conditional statement relying on the value of a variable 'subcmd' when in the chance for junking on donate it changed a variable 'mode'. Therefore when it came time to junk, it skipped this part, and left the item.
Instead of adding to the conditional statement to include this, we decided to just remove the chance at junking altogether. Everybody wins.