Remove unused ArrayRef::is_arrow #5629

Job	Run time
Rust/C++ FFI tests (tsan)	1m 55s
Rust tests (asan)	6m 31s
Rust/C++ FFI tests (asan)	2m 10s
C++ API (coverage)	1m 5s
Rust tests (tsan)	23s
Rust tests (miri)	1m 35s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	6s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	0s
DuckDB libraries available in R2	3s
Rust tests (coverage) (tests)	5m 34s
Rust tests (tsan)	5m 54s
Mirror DuckDB to R2 / Resolve DuckDB version and check R2	6s
Mirror DuckDB to R2 / Mirror DuckDB ${{ matrix.archive }} to R2	-36563s
DuckDB libraries available in R2	3s
Rust tests (coverage) (tests)	5m 34s
C++ API (coverage)	1m 5s
Rust/C++ FFI tests (asan)	2m 10s
Rust tests (miri)	1m 35s
Rust tests (asan)	6m 31s
Rust/C++ FFI tests (tsan)	1m 55s
	-33908s

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