Remove global lock from passthrough VOL callbacks #73

Job	Run time
build-and-test (--enable-api-tests, --enable-multithread --disable-hl, production)	9m 7s
build-and-test (--enable-api-tests, --enable-multithread --disable-hl, debug)	10m 21s
build-and-test (--enable-api-tests, --disable-multithread --enable-threadsafe --disable-hl, produ...	7m 39s
build-and-test (--enable-api-tests, --disable-multithread --enable-threadsafe --disable-hl, debug)	9m 10s
build-and-test (--enable-api-tests, --disable-multithread --disable-threadsafe, production)	7m 22s
build-and-test (--enable-api-tests, --disable-multithread --disable-threadsafe, debug)	8m 49s
build-and-test (--disable-api-tests, --enable-multithread --disable-hl, production)	9m 0s
build-and-test (--disable-api-tests, --enable-multithread --disable-hl, debug)	10m 35s
build-and-test (--disable-api-tests, --disable-multithread --enable-threadsafe --disable-hl, prod...	7m 43s
build-and-test (--disable-api-tests, --disable-multithread --enable-threadsafe --disable-hl, debug)	9m 5s
build-and-test (--disable-api-tests, --disable-multithread --disable-threadsafe, production)	7m 37s
build-and-test (--disable-api-tests, --disable-multithread --disable-threadsafe, debug)	8m 46s
	1h 45m 14s

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