OK, finally got all the pesky messages gone. In case anyone is interested, here are the necessary changes

In first.S, deleted the following lines
(lines 189-190)
mov al,#0x4c ! ... an 'L' ...
call display
(lines 311-312)
mov al,#0x49 ! display an 'I'
call display

In second.S, deleted the following lines(left the dokay: label there)
(lines 246-247)
mov al,#0x4c ; display an 'L'
call display
(lines 649-650)
dokay: mov bx,#ospc ; display 'O '
call say
(lines 3837+)
modified the "Loading", "BIOS data check", "successful\n" all to ""(not really necessary, but what the heck)
Deleted all references to msg_l, msg_bc, and msc_s

Thanks pinniped for pointing me in the right direction.