delv crashes processing deprecated "trusted-keys" clause in anchor file

Summary

The "trusted-keys" clause in a delv anchor file is deprecated, being replaced by "trust-anchors". However, "trusted-keys" should still be accepted, but delv crashes on encountering it. (In the examples below, the key is a locally-generated key.)

DELV version used

commit a53bc0b2

Steps to reproduce

612% delv -v
delv 9.17.1-dev
613% 
613% 
613% cat delv-1.keys
trust-anchors {
    . static-key 257 3 8 "AwEAAcOhhbamHAu0j6x+VFH/KXfKjoqtfxE6B5SYyLq4770t5FP7EOjA
    qKRFwcVswbgmn/ttZ4QBVS+3+h9VueDulG/dP1NfMj1NbrlL/PoOXTt0
    x1SMR3YX6NOZyZooJzqg/ffx13NyX8Lfj9Ni4dh+naR7lNXpL1KtMzku
    NlDgcHipnmBRlXT3tbff/VUr1MXDPTwsNZAl295VZFev3ztXI06I0bkp
    BNOErVMJLLGfqBA0q/WhibOOWelz4xG92n+hDeDyHkR3qAOkKegZePQ9
    h4GmJS+f+dSMD/1r7XvwGTznL7UjYXDqheBdZGboBEXjOAFm/U69OhG6
    ky/e2H1xPXs=";
};
614% delv -a delv-1.keys
;; validating ./NS: got insecure response; parent indicates it should be secure
;; insecurity proof failed resolving './NS/IN': 194.168.4.100#53
;; validating ./NS: got insecure response; parent indicates it should be secure
;; insecurity proof failed resolving './NS/IN': 194.168.8.100#53
;; resolution failed: insecurity proof failed
615% 
615% 
615% cat delv-2.keys
trusted-keys {
    . 257 3 8 "AwEAAcOhhbamHAu0j6x+VFH/KXfKjoqtfxE6B5SYyLq4770t5FP7EOjA
    qKRFwcVswbgmn/ttZ4QBVS+3+h9VueDulG/dP1NfMj1NbrlL/PoOXTt0
    x1SMR3YX6NOZyZooJzqg/ffx13NyX8Lfj9Ni4dh+naR7lNXpL1KtMzku
    NlDgcHipnmBRlXT3tbff/VUr1MXDPTwsNZAl295VZFev3ztXI06I0bkp
    BNOErVMJLLGfqBA0q/WhibOOWelz4xG92n+hDeDyHkR3qAOkKegZePQ9
    h4GmJS+f+dSMD/1r7XvwGTznL7UjYXDqheBdZGboBEXjOAFm/U69OhG6
    ky/e2H1xPXs=";
};
616% delv -a delv-2.keys
;; delv-2.keys:1: option 'trusted-keys' is deprecated
parser.c:1711: REQUIRE(obj != ((void*)0) && obj->type->rep == &cfg_rep_string) failed, back trace
0   libisc.1701.dylib                   0x00000001042c618a default_callback + 74
1   libisc.1701.dylib                   0x00000001042c611a isc_assertion_failed + 10
2   libisccfg.1700.dylib                0x0000000104545c58 cfg_obj_asstring + 56
3   delv                                0x00000001042a4fd9 load_keys + 457
4   delv                                0x00000001042a3dca main + 8938
5   libdyld.dylib                       0x00007fff71d2b3d5 start + 1
Abort trap: 6