Review CBMC proofs with minor issues

[adpaco-aws]

Review the following CBMC proofs:

• aws_cryptosdk_edk_list_clean_up: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_edk_list_clear: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_enc_ctx_clean_up: Low coverage in CBMC proofs involving function pointers #623
• aws_cryptosdk_enc_ctx_clear: Low coverage in CBMC proofs involving function pointers #623
• aws_cryptosdk_enc_ctx_init: Null coverage on validating functions
• aws_cryptosdk_enc_materials_destroy: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_enc_materials_new: Validating functions omitted
• aws_cryptosdk_hash_elems_array_init: aws_raise_error is omitted
• aws_cryptosdk_keyring_release: CBMC proof stubs do not replace included functions #624
• aws_cryptosdk_keyring_trace_clean_up: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_keyring_trace_clear: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_keyring_trace_copy_all: Validating functions omitted
• aws_cryptosdk_keyring_trace_eq: Static error function cannot be removed from CBMC report #625
• aws_cryptosdk_multi_keyring_add_child: aws_raise_error is omitted
• aws_cryptosdk_transfer_list: Low coverage in CBMC proofs involving function pointers #623