I doubt those are remainings of Aerys wildfire, It's way more plausible that it's Cersei's plan
First, Game of Thrones begins in 298AC, 15 years after the end of Robert's rebellion. This gives plenty of time to remove wildfire from obvious places.
Not only wildfire is extremely dangerous, but it is also scarce, as only a few alchemists know the recipe. Also, remember that massive amounts of wildfire were used both during the battle of blackwater with Stanis, and to destroy the great sept of Baelor. It seems obvious that they would use previous stock of wildfire.
During the preparation of battle of blackwater, some wildfire is found beneath dragonpit, despite being in ruins for many years.
"No, no," Hallyne squeaked, "the sums are accurate, I swear. We have been, hmmm, most fortunate, my lord Hand. Another cache of Lord Rossart's was found, more than three hundred jars. Under the Dragonpit! Some whores have been using the ruins to entertain their patrons, and one of them fell through a patch of rotted floor into a cellar. When he felt the jars, he mistook them for wine. He was so drunk he broke the seal and drank some."
"There was a prince who tried that once," said Tyrion dryly. "I haven't seen any dragons rising over the city, so it would seem it didn't work this time either." The Dragonpit atop the hill of Rhaenys had been abandoned for a century and a half. He supposed it was as good a place as any to store wildfire, and better than most, but it would have been nice if the late Lord Rossart had told someone.
A Clash of Kings - Tyrion XI
Another wildfire stock is found by Qyburn, beneath the Great Sept. If even the stock of wildfire under those buildings are found, I doubt that the stock inside more used buildings like stables remain undiscovered
Secondly, it doesn't fit the place where the mad king put wildfire
He saw traitors everywhere, and Varys was always there to point out any he might have missed. So His Grace commanded his alchemists to place caches of wildfire all over King's Landing. Beneath Baelor's Sept and the hovels of Flea Bottom, under stables and storehouses, at all seven gates, even in the cellars of the Red Keep itself.
A Storm of Swords - Jaime V
Finally, it suited well with Cersei's strategy. She allowed small folks to enter in red keep, so may Daenerys burn it, she would kill a lot of civilians. As it's obvious that once the main wall would be breached, the combat would follow on the street, she put wildfire there so Daenerys couldn't release dragonfire without hurting both civilians and buildings