Remove IAR from NXP targets without small c lib support

Toolchains should provide support for small c lib, remove IAR from the
NXP targets that don't currently do so.

Author: harrisonmutai-arm

targets/targets.json

@@ -4368,7 +4368,6 @@
         "core": "Cortex-M4F",
         "supported_toolchains": [
             "ARM",
-            "IAR",
             "GCC_ARM"
         ],
         "extra_labels": [
@@ -4435,7 +4434,6 @@
         "core": "Cortex-M4F",
         "supported_toolchains": [
             "ARM",
-            "IAR",
             "GCC_ARM"
         ],
         "extra_labels": [