In rpg_windows.js script there is a Window_Base function called drawActorHp. Around line 550. Comment out the last line which is this: this.drawCurrentAndMax(actor.hp, actor.mhp, x, y, width,
this.hpColor(actor), this.normalColor());
It should just be one line but for some reason it shows as two lines in my editor (Notepad++). To comment out a line just put // in front of it. Or you can just delete all of it.
If you don't want to mess with the core scripts, you can just put this into a new script of your own.
Window_Base.prototype.drawActorHp = function(actor, x, y, width) {
width = width || 186;
var color1 = this.hpGaugeColor1();
var color2 = this.hpGaugeColor2();
this.drawGauge(x, y, width, actor.hpRate(), color1, color2);
this.changeTextColor(this.systemColor());
this.drawText(TextManager.hpA, x, y, 44);
};