This gets rid of the last Android-specific code that directly interfaces
with INI files.

If we're in a function that isn't just going to immediately return to
Java, leaking local references can lead to problems eventually.

These files cannot compile correctly as C, so there's no reason to have
ifdefs for C compatibility.

We switched to not checking the __cplusplus macro in our JNI code some
time ago, but it seems like I forgot to remove it from these two files.

FindAllGamePaths may take a little while, and holding the
gameFileCache lock isn't actually necessary until it's time to
put the results returned by FindAllGamePaths into gameFileCache.

The downside of this change is that we have to do an extra
round of JNI in between FindAllGamePaths and Update,
but I don't think that's much of a problem.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Back when I wrote this code, I believe I set it to use a custom path
so that the cache would end up in a directory which Android considers
to be a cache directory. But nowadays the directory which Dolphin's
C++ code considers to be the cache directory is such a directory,
so there's no longer any reason to override the default path.