NimBLE deprecated four functions with ble_gattc_ prefix and they might be removed soon: mynewt-nimble#1978
Currently I think there are only two places in RIOT that use these:

Fortunately there is not much to it, because they just call the ble_gatts_ equivalent:
https://github.com/apache/mynewt-nimble/blob/bea72800c64000e9c06836e49de741ca6d318fa6/nimble/host/src/ble_gattc.c#L4717-L4725

https://github.com/apache/mynewt-nimble/blob/bea72800c64000e9c06836e49de741ca6d318fa6/nimble/host/src/ble_gattc.c#L4399-L4407

This is just a reminder for myself to do this after #21206 is merged. That PR is already pretty complicated, I don't need a potential merge conflict 👀