I don’t think this deletion of the /t/ is a feature of native English speech, although it’s done by a lot of Vietnamese speakers of English.
What you may be thinking of, though, is not deletion of the /t/, but its replacement with a glottal stop in some dialects. Many people in England will replace the /t/ in “bought” with a glottal stop before a vowel, so if they say, “I bought a loaf of bread,” the words “bought a” will sound like [bo?@]. When many native speakers pronounce words like “written” or “eaten”, we put our tongue to our alveolar ridge to say the /t/, but we delete the following vowel and then voice the /n/, so “eaten” sounds like [it?n]. This use of the glottal stop before /n/ sounds neutral to me, but in the US, using the glottal stop between vowels is stigmatized.
Also, in English word-final /t/ is preglottalized before a consonant or at the end of an utterance. We cut off our air before the tongue gets into position, and we never release the /t/. Many foreigners hear that and think we’re not pronouncing the /t/, but in fact we can hear that the consonant is there.