ovsdb-idl: Preserve change_seqno when deleting rows. #1985

Job	Run time
osx clang --disable-ssl	3m 2s
dpdk gcc	2m 1s
linux deb no dpdk	6m 13s
linux gcc --disable-ssl	2m 2s
linux clang --disable-ssl	2m 6s
linux gcc c99	2m 8s
linux clang c99	2m 8s
linux gcc test	6m 20s
linux clang test asan	10m 37s
linux clang test ubsan	7m 5s
linux gcc test --enable-shared	8m 48s
linux clang test --enable-shared	8m 56s
linux gcc test dpdk	6m 28s
linux clang test dpdk	6m 27s
linux gcc test -ljemalloc	6m 42s
linux clang test -ljemalloc	6m 30s
linux gcc --enable-afxdp	2m 3s
linux clang --enable-afxdp	2m 2s
linux gcc dpdk --enable-shared	3m 0s
linux clang dpdk --enable-shared	2m 48s
linux gcc dpdk-shared	2m 15s
linux clang dpdk-shared	2m 28s
linux gcc dpdk-shared --enable-shared	2m 58s
linux clang dpdk-shared --enable-shared	3m 3s
linux gcc m32 --disable-ssl	2m 0s
	1h 50m 10s

Provide feedback