Bottom Line: It is safe to delete obsolete printer drivers in spool\drivers. Windows caches print driver binaries for every network printer ever connected.
What is spool\drivers?
Located at C:\Windows\System32\spool\drivers\x64 (or W32X86), Windows stores printer driver packages, color profiles, and PPD files.
How to Clean Up Printer Drivers
net stop spooler
del /f /q /s C:\Windows\System32\spool\drivers\x64\3\*
net start spooler
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