freqz: Make frequency response plot visually compatible with Matlab (bug #41464) * freqz_plot.m: Eliminate the extraneous "pass band" subplot for visual compatibility with Matlab. Use y-axis labels instead of legends. Always autoscale the y-axis. Label the frequency axis in units of normalized radians or Hz depending on a new optional argument. * freqz.m: Tell freqz_plot whether the frequency vector is in normalized radians or Hz.