[platform] remove unused header file (#5538)

include/Makefile.am

@@ -83,7 +83,6 @@ dist_openthread_HEADERS = $(openthread_headers)
 ot_platform_headers                     = \
     openthread/platform/alarm-micro.h     \
     openthread/platform/alarm-milli.h     \
-    openthread/platform/ble.h             \
     openthread/platform/diag.h            \
     openthread/platform/flash.h           \
     openthread/platform/entropy.h         \

include/openthread/BUILD.gn

@@ -90,7 +90,6 @@ source_set("openthread") {
     "network_time.h",
     "platform/alarm-micro.h",
     "platform/alarm-milli.h",
-    "platform/ble.h",
     "platform/debug_uart.h",
     "platform/diag.h",
     "platform/entropy.h",