Remove RHEL conditions from spec file
    
    WebKitGTK is no longer part of ELN, so these are no longer needed.
    
    It's probably desired in EPEL, but extra dependencies can be packaged
    for EPEL.
    
    Note that -DUSE_64KB_PAGE_BLOCK=ON is also no longer needed because the
    relevant aarch64 builders are using Fedora and 4 KB page sizes. This
    significantly improves both security and performance of the aarch64
    builds.