Hi Das,
The fields which are in blue color in left panel not possible delete.
There is one possibility, Hide option, by choosing this option unwanted field/object won't transfer into BW side. it won't be part of data source in bw side. i think this will be the good to go forward.
These are t codes to hide the field for data source, RSA2,RSA6,LBWE (at ECC side)
(no idea which is your source system/ T Codes)
Thanks