So basically, the Monitor destroyed Earth-90. This means that all heroic deeds and accomplishments that the 1990 Barry Allen (John Wesley Shipp) got on there had been 100% USELESS, because the entire Earth was eventually destroyed in a blink of the eye.
Plus, Barry Allen (JWS) sacrificed himself.
The entire 1990 Flash series has been obliterated just for stupid storytelling purposes related to the Arrowverse.