In SERVER-74747 we removed both:
 - The logic to support numInitialChunks parameter
 - The parameter itself from the requests IDL

While starting from  7.2 is it totally fine to ignore the parameter, we can't really remove the parameter itself due to backward incompatibility with previous versions.

In particular in 7.0 the mongos was always sending the __ _shardsvrShardCollection command with a default value 0. This means that request always contain numInitialChunk: 0 , while in 7.2 since we removed completely the parameter the request will not have this parameter at all.

As a consequence the two requests do not match between one version and the other.