Fix setenv() of non-SDL2 bootstrap

[j-devel]

Fixes #1702. This is regression related to #1690. For non-SDL2 bootstrap, we should not use SDL_setenv() here; instead, use the plain setenv() as previously. Sorry that I missed testing this bootstrap case.

Before fix:

/home/a/.local/share/python-for-android/build/bootstrap_builds/webview-python2/jni/application/src/start.c:471: error: undefined reference to 'SDL_setenv'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)

After fix: No compile errors regarding this issue.

[AndreMiras]

Yes we definitely need some runtime automated testing. Thank you for addressing that regression!

[AndreMiras]

Thanks!