Removing the USE_ES6_IMPORT_META setting

[Sam Clegg]

Hi all,

I'm hoping to remove this setting in the next release: https://github.com/emscripten-core/emscripten/pull/23171.

Hopefully since `import.meta` has not been stage 4 for almost 5 years it should be safe to depend on it everywhere.   Is anyone still depending on this setting?

cheers,

sam