rust: macros: remove `module!`'s deprecated `author` key

Commit 38559da6 ("rust: module: introduce `authors` key") introduced
a new `authors` key to support multiple module authors, while keeping
the old `author` key for backward compatibility.

Now that most in-tree modules have migrated to `authors`, remove:
1. The deprecated `author` key support from the module macro
2. Legacy `author` entries from remaining modules

Signed-off-by: Guilherme Giacomo Simoes <trintaeoitogc@gmail.com>
Acked-by: Andreas Hindborg <a.hindborg@kernel.org>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20250609122200.179307-1-trintaeoitogc@gmail.com


[ Reworded slightly. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>