The message tar: Removing '/' from member names is being output by tar to stderr. You can redirect stderr on the command like with something like this:

tar -cz /usr/fweb/xyz/abc > /usr/fweb/xyz/aa.tar.gz 2> /dev/null
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The 2> redirects stderr the same way > redirects stderr. So the above command is telling the shell to send stderr to /dev/null which on most systems, just throws it away.

Put that command in your `` in your script, and see if it works.