Install Windows 10 on MacBook Pro 8.1
Your Mac does not officially support Windows 10. However, this does not mean Windows 10 can not be installed on your model Mac. Here are some points to be aware of.


With the newer versions of macOS, you can download the Windows Support Software for your Mac by using the Boot Camp Assistant application. This may be the same as the Boot Camp Support Software 5.1.5621.
Make sure the Windows Support Software have beed copied to the Windows 10 installer flash drive before installing Windows 10.
You want to have first installed the latest version of High Sierra. This will insure you have the latest firmware updates. (Firmware updates are included in the latest versions of macOS.)
You would be better off installing Windows 10 to BIOS boot. Most likely the Windows Support Software for you model Mac was designed for BIOS booting and may not work properly if you install Windows to EFI boot.
The Windows Support Software for your Mac may contain a BootCamp.msi file that is to old to be used with the latest versions of Windows 10. See the question WDF VIOLATION Blue Screen after Upgrading Mac to Windows 10 May 2019 Update (1903) Edition.


If you do not want or need macOS installed on your Mac, then you can just have Windows 10 installed. However, you would be better off first installing Windows 10 for a dual boot with macOS. One possible procedure which might work with your Mac is given as the answer to the question How to install Windows 10 into a 2011 iMac without using the Boot Camp Assistant, an optical (DVD) drive or third party tools?. Once you have booted to a working Windows 10, you can use the Windows 10 flash drive installer to reinstall Windows 10. This time you will need to erase all partitions to remove macOS before installing.