Revert "[12.x] Update "Number::fileSize" to use correct prefix and add prefix param"

[ziadoz]

Reverts #55678

The changes made here are breaking. The useBinaryPrefix parameter is false by default, which means the base is now 1000 instead of 1024. Defaulting it to true doesn't fix the issue though, as the units for 1024 will be KiB instead of KB.

This is breaking various frontend tests in my web app when Dependabot tries to update Laravel.

// Before
> Number::fileSize(1024)
= "1 KB"

// After
> Number::fileSize(1024, useBinaryPrefix: true)
= "1 KiB"