[LABS-282] Remove unnecessary private key access from get_public_keys

[Quexington]

Just a small improvement noticed while doing a pass over the wallet RPC

[coveralls-official]

Pull Request Test Coverage Report for Build 18601315505

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 25 unchanged lines in 7 files lost coverage.
• Overall coverage decreased (-0.01%) to 90.833%

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Files with Coverage Reduction	New Missed Lines	%
chia/full_node/full_node_api.py	1	85.95%
chia/wallet/wallet_rpc_api.py	1	92.11%
chia/full_node/full_node.py	3	86.85%
chia/_tests/core/util/test_lockfile.py	3	88.89%
chia/introducer/introducer.py	4	83.62%
chia/server/node_discovery.py	6	79.61%
chia/server/address_manager.py	7	92.84%

Totals
Change from base Build 18601081112:	-0.01%
Covered Lines:	102296
Relevant Lines:	112461

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💛 - Coveralls