Delete hack to always do codegen for templates if -debug is used

[atilaneves]

This PR deletes code that special cases -debug/-unittest when considering whether or not to do codegen for templates in non-root modules. It also deletes a dmd test that's no longer necessary due to Phobos having been updated in the meanwhile (there used to be a debug block in std.range that caused linker errors due to template instantiation with -debug).

Relevant issues and PR:

https://issues.dlang.org/show_bug.cgi?id=12661
https://issues.dlang.org/show_bug.cgi?id=15230
#4944

[atilaneves]

Blocked by dlang/phobos#7439

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If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#10968"

[UplinkCoder]

This caused a ICE to appear in our code.

[UplinkCoder]

also why are you deleting this tests ... they should still pass after this PR?

[wilzbach]

This caused a ICE to appear in our code.

Is it possible to isolate the code to a reduced example?

[UplinkCoder]

Is it possible to isolate the code to a reduced example?

possible. yes.

My comment is less about a particular example, and more about doing invasive changes in poorly understood systems ...
I can reduce it for completeness sake.

[atilaneves]

also why are you deleting this tests ... they should still pass after this PR?

They weren't very good tests and not relevant anymore. They were testing that there were no linker failures with Phobos code that doesn't even exist anymore.

[WalterBright]

This has caused a regression https://issues.dlang.org/show_bug.cgi?id=15985

[ibuclaw]

This has caused a regression https://issues.dlang.org/show_bug.cgi?id=15985

Issue was created in 2016, this PR was created in 2020. Unless I've forgotten how time works, no it didn't. :-)