Android - Removing apk of inbuilt apps completely (without rooting)

Unfortunately, that is just not possible. The apk of system apps resides within system partition. The privileges (access rights) required to make changes in system partition are not given to ordinary users. We can only gain such higher privilege through rooting.

That said, if you are dealing with space issues than you are looking at wrong front. System partition has nothing to do with those space issues since only a system wide update/upgrade makes changes in it. They are caused by data partition. It is possible that you may have updated some system apps, so now, they would be having an apk in system partition and another apk (the latest update) in the data partition (now that is one precious space). You can delete the ones in data partition by disabling that system app. When you attempt to do that you would get something like this:

OK, and the apk from the data partition would get deleted.