Cleanup and provide only one underlying hex encoding/decoding implementation

[ttjsu-aws]

Problem:

We currently have 3 implementation of hex within s2n that cater to different internal data_structures/use-cases, namely:

S2N_RESULT s2n_key_log_hex_encode(struct s2n_stuffer *output, uint8_t *bytes, size_t len);
extern int s2n_stuffer_read_hex(struct s2n_stuffer *stuffer, struct s2n_stuffer *out, uint32_t n);
extern int s2n_hex_string_to_bytes(const uint8_t *str, struct s2n_blob *blob);
int s2n_str_hex_to_bytes(const uint8_t *hex, uint8_t *out_bytes, uint32_t *out_bytes_len);

• s2n_key_log_hex_encode
• s2n_stuffer_read_hex
• s2n_hex_string_to_bytes

We need to cleanup these hex functions and provide only one underlying solution for hex encoding and decoding.

Solution:

Cleanup the utility hex encoding and decoding implementations and provide only one underlying solution for hex encoding and decoding.

• Does this change what S2N sends over the wire? No
• Does this change any public APIs? No, utility functions
• Which versions of TLS will this impact? All.