Even budget phones are pretty good these days, but most of them suffer from an unfortunate lack of storage. 8GB seems to be the standard (with some going as low as 4GB), and that isn't helped by manufacturers' habit of including a ton of apps you might not need or want. Sony got some negative feedback for the Xperia M4 Aqua's 8GB on the base model, but it looks like they've taken it to heart: the latest update to the phone removes quite a few previously standard apps, freeing up some much-needed storage.
Xperia Blog did a pretty great breakdown on the phone's original storage situation, which left just 1.25GB of free space for users after Android 5.0 and all the included apps. According to a recent post on Sony's support site for the standard and dual-SIM versions of the M4 Aqua, the latest software update (version 26.1.A.2.167 and 26.1.B.2.147, respectively) will remove the following apps, assuming you've never updated them before:
Google News & Weather
Google Play Games
The usual bug fixes are also included.
Odds are pretty good that you've updated some or all of these apps, if only to get rid of the notifications - presumably resetting your phone before you take the update will take care of that issue. It's not much, but it's nice to see that Sony isn't completely ignoring its customers on this one.