[DellEMC S5248f] Remove duplicate ipmihelper.py (sonic-net#10455)

Why I did it
To remove the ipmihelper.py in S5248f directory to prevent the image label being marked 'dirty', due to the file being replaced by the ipmihelper.py in common folder during build.

How I did it
Remove ipmihelper.py in S5248f directory.

How to verify it
Build a broadcom image and verify that the tracked files are not modified.

Which release branch to backport (provide reason below if selected)
 201811
 201911
 202006
 202012
 202106
 202111
Description for the changelog
DellEMC S5248f : Remove duplicate ipmihelper.py

Link to config_db schema for YANG module changes
A picture of a cute animal (not mandatory but encouraged)