Remove unused btm_ble_rand_enc_complete

LE Rand only gets sent with its own callback.

LE Encrypt (0x2017) never gets sent. It has been
replaced by Enable Encryption (0x2019).

Bug: 283254594
Test: mma -j32
Change-Id: Ibb3fede282adab261ed0fb7035e470e370029e63
Merged-In: I763c759f5e89b6edb5c269a6024e254ed0d5d77b