[6.0.x] Remove libicu build and update list of Swift runtime libraries to be de-duplicated

[finagolfin]

Explanation: Libicu is entirely unused on non-Darwin platforms too since the Foundation re-core to use _FoundationICU, so shave 35 MB off the 6.0 non-Darwin toolchains by removing it. Also, update the list of libraries that are deduplicated by the autolink-extract tool.

Scope: Only affects code for non-Darwin platforms, that is now entirely unused.

Issue: None

Original PRs: #75262, #75342, and #76224

Risk: Very low

Testing: Passed all CI on trunk

Reviewer: @jmschonfeld @compnerd @parkera @etcwilde

We are unnecessarily still shipping libicu in the 6.0 toolchains despite having another copy in lib_FoundationICU. This was removed in 6.1 months ago without a problem.

[finagolfin]

@jmschonfeld, need a CI run here.

[jmschonfeld]

@swift-ci please test

[finagolfin]

Passed CI, just needs approval from @compnerd and other owners.

[finagolfin]

@shahmishal, let me know what you think as the linux platform manager about shaving these unused libraries off the 6.0 toolchain in a patch release.

[shahmishal]

I would like to get a review from @parkera and @airspeedswift.

[parkera]

I don't want to aggressively cherry pick this back without any evidence that it resolves the named bug. We're already doing it on main, though.

[finagolfin]

@parkera, this has nothing to do with any bug, I think you might have got this mixed up with #76606. This is just about a simple cleanup on the toolchain for libicu libraries that are now unused on linux and Windows after the Foundation re-core, which uses _FoundationICU instead.

[parkera]

Ok, thanks

[finagolfin]

Ping @shahmishal, do we need anyone else to sign off? I think you and I pinged all relevant reviewers weeks ago.

[finagolfin]

Ping @airspeedswift, I think Mishal just wanted you to sign off.

[finagolfin]

Ping @shahmishal, would be good to get this in before the next patch release.

[shahmishal]

cc: @airspeedswift

[DougGregor]

It's been a while, so re-running CI before merging

[DougGregor]

@swift-ci please test

[finagolfin]

Passed CI, ready for merge.