With the change from using archive files to using object files in PR #14754, the module `esp_wifi_enterprise` was no longer compilable. The reason for this was that the file `bignum.c` was present in two different vendor sub-directories and created two identical object files, which then led to a symbol conflict when linking. This commit removes one of these identical files. The one that is used in all `esp_wifi` variants is kept, the one that is only used in `esp_wifi_enterprise` is dropped.
Renames crypto functions of ESP32 SDK in vendor code to resolve the conflicts between `wpa-supplicant` crypto functions and RIOT's `crypto` and `hashes` modules.
To resolve the conflicts between `wpa-supplicant` crypto functions (part of the ESP32 SDK) and RIOT's `crypto` and `hashes` modules, the crypto function headers from ESP32 SDK are added to vendor code and the crypto functions are renamed using the prefix `wpa_`.
