SPI_pfree 释放之前使用 SPI_palloc 或 SPI_repalloc 分配的内存。
SPI_pfree frees memory previously allocated using SPI_palloc or SPI_repalloc.
此函数不再与普通的 pfree 不同。保留它只是为了保持现有代码的向后兼容性。
This function is no longer different from plain pfree. It’s kept just for backward compatibility of existing code.