[IOT-2465] Fix DELETE request impl for cred
[IOT-2465] Fix DELETE request impl for cred

Verified using CTT 1.5.11 test CT1.7.9.3
DELETE delete all credentials return PASSED

Change-Id: Ie52c6af9fb9205a650b766acf0084e0ac2dcdcf1
Signed-off-by: Andrii Shtompel <25499a78f7e7032392a327573ae90c1e2a94b983@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/21403
Reviewed-by: Aleksey Volkov <a27d9cdf263d3bb0a7e1b2122425c0a535a3f64c@samsung.com>
Tested-by: jenkins-iotivity <d95b56ce41a2e1ac4cecdd398defd7414407cc08@iotivity.org>
Reviewed-by: Nathan Heldt-Sheller <214cad4ab375dc179217f558f8b9854a693faf7f@intel.com>
Reviewed-by: Oleksii Beketov <8b8402ce463b3ba6094920b3493fffa206a8eaa1@samsung.com>
Reviewed-by: Randeep Singh <46ce9385024397d3e4d9ed63be2e0a0d801e95b7@samsung.com>

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