Remove get_cipher_by_char and put_cipher_by_char.

Without SSLv2, all cipher suite values are 2 bytes. Represent them as a
uint16_t and make all functions pass those around rather than pointers.

This removes SSL_CIPHER_find as it's unused.

Change-Id: Iea0b75abee4352a8333a4b8e39a161430ae55ea6
Reviewed-on: https://boringssl-review.googlesource.com/1259
Reviewed-by: Adam Langley <agl@google.com>