[2025-TF2-SDK Update] Update server setup documentation (for 64-bits Source-1)

[nullsystem]

Since the update moved from 32-bits to 64-bits and have lots of fixes, the server setup documentation for both Windows and Linux need to be updated. Likewise I think the jank workarounds can be omitted now in the instructions, but also you'll need to bare in mind the extra x64 and linux64 directories for libraries/bins as well as _x64 and _linux64 postfixed executables.

[nullsystem]

ValveSoftware/source-sdk-2013#713
srcds_linux64 and srcds_win64.exe has been misplaced in the client depot instead.
bin/linux64/libsteam_api.so also missing.

[nullsystem]

NOTE: Dedicated servers on Linux actually works without code change, just need to update instructions properly. Will also update the 12.0-prealpha release note to reflect that.