perf: use starlark string.removeprefix

[jbedard]

I think this is even in 5.1 and ok for rules_ts? bazelbuild/bazel@50bb742

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Type of change

• Refactor (a code change that neither fixes a bug or adds a new feature)
• Performance (a code change that improves performance)

Test plan

• Covered by existing test cases

[alexeagle]

This seems fine, are you starting from some profile of the analysis time that showed you this code was inefficient?

[jbedard]

I know creating the large temp arrays has a side-effect. The temp array in this for loop is tiny, but the method is invoked frequently.

This change on it's own made no significant difference (when using ts_project + swc) but aspect-build/rules_swc#234, aspect-build/rules_swc@273eace and aspect-build/rules_swc@6bf6610 had very significant improvements so I'd prefer making this a pattern even if individual cases are not always significant.

[jbedard]

Also repeating path.removeprefix("external/") 3x should make this functionally the same, but points out that we probably don't need it 3x?