legacy: Truncate hci/include/userial

Currently still included by:
hardware/broadcom/libbt/include/userial_vendor.h
vendor/amlogic/common/wifi_bt/bluetooth/realtek/rtkbt/code/libbt-vendor/include/userial_vendor.h
vendor/amlogic/common/wifi_bt/bluetooth/broadcom/vendor/include/userial_vendor.h
vendor/amlogic/common/wifi_bt/bluetooth/amlogic/aml_libbt-vendor/include/userial_vendor.h

Bug: 197150934
Tag: #refactor
Test: gd/cert/run
BYPASS_LONG_LINES_REASON: Bluetooth likes 120 lines

Change-Id: If7b528138510851fb26b9bcdc60017672110e430