The definitions were being defined already by `BootInfo.h` and that was
being included here via transitive includes. The extern definitions of
the variables do not have the `READONLY_AFTER_INIT` attribute in
`BootInfo.h`. This causes conflicting definitions of the same variable.
The `READONLY_AFTER_INIT` specifier is not needed for extern variables
as it only effects their linkage, not their actual use, so just use the
versions in `BootInfo.h` instead of re-declaring.
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