Convert the RAdmin format to thin around dynamic_1010, or optimize

The RAdmin format uses scalar MD5 code. Equivalent functionality is implemented in dynamic_1010 with SIMD. We could convert it similarly to what we already did with a few other formats:

$ grep 'thin format' *.c
NS_fmt_plug.c: * Changed to thin format dynamic_2004, Dec 2014, JimF
asaMD5_fmt_plug.c: * Converted to thin format, into $dynamic_20$ format.
mediawiki_fmt_plug.c: * This thin format will change the above line into this, for hooking
pixMD5_fmt_plug.c: * Converted to thin format, into $dynamic_19$ format.

Alternatively, optimize it to use SIMD directly, and perhaps to reverse MD5 steps for the second block (something dynamic doesn't do - but maybe it could be enhanced, too).

Compare the RAdmin implementation with dynamic_1010 and the thin-format examples named in the issue, including NS_fmt_plug.c, asaMD5_fmt_plug.c, mediawiki_fmt_plug.c, and pixMD5_fmt_plug.c. Determine whether the format should become a thin wrapper or receive direct SIMD and reversed-MD5-step optimization; done means the chosen approach is implemented and its behavior remains equivalent.