unbindTexture2D(texture, unit) {
		if (typeof unit === "undefined") {
			unit = this.boundTextures.indexOf(texture);
		}
		if (unit !== -1) {
			delete this.boundTextures[unit];
			if (unit === this.currentTextureUnit) {
				this.currentTextureUnit = -1;
			}
		}
		return unit;
	}
unbind the given WebGL texture, forcing it to be reuploaded
@param {WebGLTexture} [texture] - a WebGL texture
@param {number} [unit] - a WebGL texture
@returns {number} unit the unit number that was associated with the given texture