[perf] Add async_mode restriction to ti.sync() of external_arrays in class Kernel (#3535)
[perf] Add async_mode restriction to ti.sync() of external_arrays in class Kernel (#3535)

* [perf] Remove ti.sync() for external_arrays

* Update python/taichi/lang/kernel_impl.py

Co-authored-by: Yi Xu <9006615d4a14d4a36732e630a0ff5f99f65fadf4@foxmail.com>

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Co-authored-by: Yi Xu <9006615d4a14d4a36732e630a0ff5f99f65fadf4@foxmail.com>
Co-authored-by: Taichi Gardener <52844ac7498fba84f633481a7c3ae54491811c81@gmail.com>
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi