Some of the content files supported in both iC and CC include:
.imotion
.imotionplus
.imtl
.imtlplus
.iprop
.rlmotion
.cclightRoom

If you don't want to show them in CC, then refer to the following steps :
1) Multi-select and right-click --> "Mark as Invisible Content"
2) Go to the right-top menu --> Settings --> Check the "Hide Invisible Content".
3) Now the items marked as invisible will be hidden in the Smart Gallery.

If you want to keep them and don't want to download content repeatedly in iC or CC,
Then try this new SGv1.2 feature - Contents Sharing for iClone and Character Creator
This can help you make CC and IC share the same content folder :
https://manual.reallusion.com/Smart_Gallery_Plug_in/ENU/1.2/09_Scenarios_and_Solutions/Contents-Sharing-for-iC-and-CC.htm