Flags cleanup

[mhegazy]

Now that we are using the config action everywhere there is a lot of flags that were manually passed that are not needed any more.

• Remove unused inputs from the action
• Remove unused flags from the matrix definition
• Remove Platform in favor of a single property os
• Remove compiler_target in favor of triple

Downstream job: https://github.com/thebrowsercompany/swift-build/actions/runs/17679457004

[mhegazy]

my next step is remove custom matrixes from jobs in swift-toolchain.yml so we are always using host/target matrix when applicable, and then simplify Android handeling in the script.

[compnerd]

Nice! I like red! I wonder if the matrix is now simple enough to inline instead of having the two layer thing.