Cleaning up include file inconsistencies

[Dr. Matthias St. Pierre]

Hi all,

pull request #9274 started out as a task to clean up inconsistencies in the naming
of the include guards. It turned out that there are also some inconsistencies in the
naming of the include files.

Please take a look at the general discussion starting at
https://github.com/openssl/openssl/pull/9274#issuecomment-508824668
between Bernd and me.

In particular, in
https://github.com/openssl/openssl/pull/9274#issuecomment-508826903 and
following the question was raised whether all local `*_lcl.h` files should be renamed
to `*_locl.h` for consistency reasons, and the pros and cons discussed. 
The latter choice was suggested by a source tree vote:

   ~/src/openssl$ find -name '*_lcl.h' | wc -l
   19
    ~/src/openssl$ find -name '*_locl.h' | wc -l
    30

What's your opinion about renaming of those files?

Matthias