sample: remove unused pIotCoreThingName #860

Job	Run time
mac-os-build-clang	13m 54s
address-sanitizer	8m 42s
clang-format-check	19s
linux-gcc-4_4	8m 19s
linux-gcc-code-coverage	8m 10s
mac-os-build-gcc	26m 6s
static-build-linux	9m 16s
static-build-mac	13m 28s
thread-sanitizer	8m 41s
undefined-behavior-sanitizer	8m 57s
arm32-cross-compilation	7m 19s
arm64-cross-compilation	5m 57s
linux-aarch64-cross-compilation	7m 10s
mbedtls-ubuntu-clang	6m 9s
mbedtls-ubuntu-gcc	6m 12s
sample-check	5s
ubuntu-os-build	7m 59s
windows-msvc-openssl	20m 49s
	2h 47m 32s

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