kernel: Eliminate variable shadowing

kernel: Delete unused files

externals: Update SDL to 107db2d8

Building it as a shared library causes issues distributing it to an
AppImage, since linuxdeploy expects the executable to only dynamically
link to system libraries. Additionally, simply dynamically linking to a
library in the binary directory is bound to cause issues.

Solution is to use SDL's CMake switches and build it statically. We also
alias `SDL2` to `SDL2-static` on the external submodule for
compatibility with the rest of the project.

In light of 72a49c2b, the SDL submodule also needs updated. Updates
to the same commit used by the SDL package in ext-windows-bin.

Now that the large kernel refactor is merged, we can eliminate the
remaining variable shadowing cases.

- Improves native Switch JoyCon/Pro Controller support.

Kernel Rework: Migrate kernel objects to KAutoObject

ldr: Simplify memory copy within LoadNro()

We can use the dedicated memory function for performing copies instead
of reading into a temporary buffer and then immediately writing it back
out to memory.

Eliminates a bit of heap memory churn.

fixup! common: intrusive_red_black_tree: Disable static_assert that will not evaluate as constant on MSVC.