I can understand that you would like to remove the line in the errorbar legend symbol.
Although I am not aware the proper solution, I have a possible workaround which might be helpful:
You can remove the 'k' parameter from the errorbar function, and set the 'LineStyle' parameter to 'None'. This will avoid plotting the line in the graph. However, if you still want to plot the line, you can use 'hold on' command in matlab and plot the line separately.
You can check to the following code for reference:
x = 1:10:100;
y = [20 30 45 40 60 65 80 75 95 90];
yneg = [1 3 5 3 5 3 6 4 3 3];
ypos = [2 5 3 5 2 5 2 2 5 5];
xneg = [1 3 5 3 5 3 6 4 3 3];
xpos = [2 5 3 5 2 5 2 2 5 5];
errorbar(x,y,yneg,ypos,xneg,xpos,'LineStyle','none')
hold on
plot(x,y)
legend({'Line_1'})
