What should I do about my vow to perform two rak'ahs of "Salat Al-Shukr" (Prayer of Gratitude) for the rest of my life, after learning that there is no prayer by this name?

There is no 'Prayer of Gratitude' (Salat al-Shukr) according to the soundest opinions of the scholars; rather, what is transmitted is the 'Prostration of Gratitude' (Sujud al-Shukr). The jurists have stipulated that whoever makes an unlawful vow is not obligated to fulfill it, and it is nullified. As for one who vows an unlawful act of worship, such as the 'Prayer of Gratitude,' the more apparent view is that he must offer an expiation for breaking an oath (kaffarat yamin).