Update `RISCV_SCAN_DELAY_MAX` to `UINT_MAX`

[en-sc]

https://github.com/riscv-collab/riscv-openocd/blob/3bed4c8015b319b97e6651a383db9ae001f11aa9/src/target/riscv/batch.h#L48-L55

The reason for making RISCV_SCAN_DELAY_MAX INT_MAX / 2 no longer holds -- jtag_add_runtest() accepts an unsigned int since 0847a4d7fb9809a9bb36ba0965f43cb9d43ca2f3. https://github.com/riscv-collab/riscv-openocd/blob/3bed4c8015b319b97e6651a383db9ae001f11aa9/src/jtag/core.c#L592

This makes it possible to increase RISCV_SCAN_DELAY_MAX and remove/simplify checks.