Rearrange code examples in docs for clarity

Rearrange code examples in docs for clarity

The introduction of a deprecation notice between the header include
line and the function prototypes left the inclusion in the previous
block.  Move the #include to after the deprecation notice to ensure
that the headers is included together with the corresponding MDX_y*
functions.

Reviewed-by: Neil Horman <nhorman@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/24864)