A few minor mbtiles-copier cleanups #1705

Job	Run time
Build x86_64-unknown-linux-gnu	24m 5s
Build x86_64-pc-windows-msvc	21m 27s
Build x86_64-apple-darwin	12m 56s
Build aarch64-apple-darwin	16m 17s
Test Legacy DB (postgis/postgis:11-3.0-alpine, postgres, disable)	1m 55s
Test Legacy DB (postgis/postgis:14-3.3-alpine, postgres, disable)	2m 12s
Test Legacy DB (postgis/postgis:15-3.3, postgres -c ssl=on -c ssl_cert_file=/etc/ssl/certs/ssl-ce...	2m 1s
Test & package x86_64-unknown-linux-gnu	2m 40s
Test & package x86_64-pc-windows-msvc	1m 17s
Test & package x86_64-apple-darwin	2m 48s
Test & package aarch64-apple-darwin	6s
	1h 27m 44s

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