Usually, (assuming the song or poem is good at grammar), you can determine the tense of the verb by simple contextual clues, but after clicking on one of your links (and, thankfully, having never heard the song) I found that his verbs are all over the place ("you rained on my parade," "you think you broke my heart," "I'll be movin' on"), so I can't tell whether didn't or don't was used without listening to the song, which I am not doing.
Technically, the sentence "My mama don't like you, but she likes everyone" is not grammatically correct; the use of don't instead of doesn't for the third person singular is, in my experience, pretty common slang. Also, "doesn't" has too many syllables. "Didn't" instead of "don't" is correct; it has too many syllables and creates an inconsistent verb tense like the rest of the song.
In other words, it isn't.