Remove StringKind::FString and StringKind::RawFString

[dhruvmanila]

Summary

This PR removes the now unused StringKind::FString and StringKind::RawFString
enum variants.

Test Plan

cargo test

[dhruvmanila]

Current dependencies on/for this PR:

• main
  • PR Add support for PEP 701 #7376
    • PR Update logical line rules for the new f-string tokens #7690
    • PR Remove StringKind::FString and StringKind::RawFString #7667 👈
    • PR Ignore quote escapes in expression part of f-string #7597
    • PR Separate Q003 to accomodate f-string context #7588
      • PR Update Q000, Q001 with the new f-string tokens #7589
    • PR Use the new f-string tokens in string formatting #7586
    • PR Update ISC001, ISC002 to check in f-strings #7515
    • PR Update RUF001, RUF003 to check in f-strings #7477
    • PR Update PLE2510, PLE2512-2515 to check in f-strings #7387
    • PR Allow NUL character in f-strings #7378
    • PR Update W605 to check in f-strings #7329
    • PR Update Stylist quote detection with new f-string token #7328
    • PR Update F541 to use new f-string tokens #7327
    • PR Detect noqa directives for multi-line f-strings #7326
    • PR Update Indexer to use new f-string tokens #7325

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[dhruvmanila]

Sorry, I messed up my last rebase 😓

[codspeed-hq]

CodSpeed Performance Report

Merging #7667 will degrade performances by 3.88%

_{Comparing dhruv/remove-fstring-kind (a9230df) with dhruv/pep-701 (917cace)}

Summary

❌ 1 regressions
✅ 24 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	dhruv/pep-701	dhruv/remove-fstring-kind	Change
❌	linter/default-rules[large/dataset.py]	91.9 ms	95.6 ms	-3.88%