dyndbg-docs: eschew file /full/path query in docs

dyndbg-docs: eschew file /full/path query in docs

Regarding:
commit 47ff819f5eca ("dynamic_debug: add trim_prefix() to provide source-root relative paths")
commit 4adbdcad7f07 ("kbuild: use -fmacro-prefix-map to make __FILE__ a relative path")

2nd commit broke dynamic-debug's "file $fullpath" query form, but
nobody noticed because 1st commit had trimmed prefixes from
control-file output, so the click-copy-pasting of fullpaths into new
queries had ceased; that query form became unused.

Removing the function is cleanest, but it could be useful in
old-compiler corner cases, where __FILE__ still has /full/path,
and it safely does nothing otherwize.

So instead, quietly deprecate "file /full/path" query form, by
removing all /full/paths examples in the docs.  I skipped adding a
back-compat note.

Acked-by: <jbaron@akamai.com>
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Link: https://lore.kernel.org/r/20200719231058.1586423-2-jim.cromie@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>