Fix up rtweekend.h introduction #1473
Description
In book 1, once we introduce rtweekend.h, we need to include the changes to all other existing header files to include it, and to remove now-unneeded declarations and definitions.
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In book 1, once we introduce rtweekend.h, we need to include the changes to all other existing header files to include it, and to remove now-unneeded declarations and definitions.