Assuming there are no spaces in text column itself, try SELECT REPLACE(GROUP_CONCAT(txt),',','') AS txt INTO OUTFILE 'test.txt' FROM tbl ;
If there are spaces in data then wrap one more REPLACE( ,' ','') around
if you run into limit (how many rows are to be GROUP_CONCATinated then it's best to use following if you are using Unix like OS
cat 'test.txt' | tr -d '\t'