[commit] cleanup stale exec.{h|c} xfer_memory comments.

[Eli Zaretskii]

> From: Pedro Alves <pedro@codesourcery.com>
> Date: Fri, 12 Jun 2009 19:43:07 +0100
> 
> The comment describing section_table_xfer_memory_partial is actually
> still describing the old xfer_memory.  This removes that stale
> description, and adjusts the description in the header a bit better
> to current reality.

Is the convention to describe functions in headers?  That's reasonable
for data structures, but we have a lot of functions documented right
before their source, not in the headers.  I find the documentation in
the .c files easier to use, because you don't need to consult another
file.  This is C, not C++, so the interface and the implementation are
not separated.