It correctly tacks a 0 byte on the end if that's what you mean, of course cleaning up the unused space would be outside of the task at hand.
Maybe I'll look like a complete idiot soon if it transpires I've completely missed the 'gotcha' ;)
// esi -> asciiz string
// cl = character to remove
mov edi, esi
cld
loop1:
lodsb // Load the byte from [esi] into al
or al, al
jz alldone
cmp al, cl
je loop1 // Skip this byte, since it's one we want to remove
stosb // Store the byte at [edi] from al
jmp loop1 // Loop around for the next byte
alldone:
xor al, al
stosb // 0 terminate it
Still, likely my memory is at fault.
But your final solution is clearer than mine. While it uses an extra variable (register), it avoids looking up the same thing twice. So... more efficient and clearer.
BTW: TIL char * a = "hello"; doesn't work in C (I think it doesn't allocate memory). I'm actually happy enough that I could solve this at all, not having used C for 20 years ...old