remove imxrt from makebuild

Author: hathach

.github/workflows/build_arm.yml

@@ -33,7 +33,6 @@ jobs:
         family:
         # Alphabetical order
         - 'broadcom_32bit'
-        - 'imxrt'
         - 'kinetis_k32 kinetis_kl'
         - 'lpc11 lpc13 lpc15 lpc17 lpc18'
         - 'lpc51 lpc54 lpc55'