[BUG] Have TIFlash use CCS installation version of board_ids.json for default device lookup

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Describe the bug
Currently TIFlash uses a provided version of board_ids.json for device-serno look up by default. This causes us to have to maintain this file and keep it up to date with every new device. Instead, we should remove the provided board_ids.json file. TIFlash should first load the board_ids.json file provided with CCS installation. Then if a board_ids.json file exists in the ~/.tiflash folder (in case user wants to place a custom file to use), and load these entries into the lookup table. Any duplicate keys will be replaced by the custom file.

Possible Fix

1. Remove the board_ids.json file provided with tiflash
2. Have get_devicexml_from_serno() first load the provided board_ids.json file provided in CCS installation. Then if a "board_ids.json" file exist in ~/.tiflash folder, this file will be loaded into the same dictionary; updating/replacing any duplicate entries.