Cannot remove one of the x-ticks from a 2x1 subplot.

[generalzu10]

I figured out the problem. I posted my answer to Stack Exchange. Just gonna leave a copy here.

#setup second axis of plot 2
    ax22.clear()
    ln4 = ax22.plot(x2,y22,colors[1],label = 'CO2(%)')
    ax22.tick_params(axis = 'y',labelcolor = colors[1])

    #---------------------------------------------#
    #set the x-axis tick labels visibility to False
    plt.setp(ax21.get_xticklabels(),visible = False)
    #----------------------------------------------#
    
    #keep two legends from the two axes together. legends belong to an axis. In our case, we have two y-axis, so two separate legend made rather than together
    lns2 = ln3 + ln4
    labs2 = [l.get_label() for l in lns2]
    ax21.legend(lns2,labs2,bbox_to_anchor = (0,-0.1,1,0)
                # (0,1.02,1,0.102)
                ,loc = 'lower left',ncol = 3,borderaxespad = 0)

Final picture:

What changed: added the line plt.setp(ax21.get_xticklabels(),visible = False) and change bbox_to_anchor parameters to (0,-0.1,1,0)