Remove unneeded variable reference in FTL run script

[PromoFaux]

What does this PR aim to accomplish?:

Noted that CAP_STR is empty since 776bac7

Adding in the following on a local build proved it:

echo "-----------------"
echo ${CAP_STR:1}
echo "-----------------"

Outputs:

pihole  | -----------------
pihole  | 
pihole  | -----------------

However, there shouldn't be anything that needs fixing here as the caps are already set further up the script

pihole  |   [i] Applying the following caps to pihole-FTL:
pihole  |         * CAP_CHOWN
pihole  |         * CAP_NET_BIND_SERVICE
pihole  |         * CAP_NET_RAW
pihole  |         * CAP_NET_ADMIN

To note: Currently we are calling:

--inh=${CAP_STR:1} --addamb=${CAP_STR:1}

or - actually

--inh= --addamb=

And nobody has complained it's not working... The conversation around moving the stuff back out into bash_function.sh happened here: #1175 (comment)

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