Remove support for the deprecated torchtext legacy

[carmocca]

What does this PR do?

Remove support for the deprecated torchtext legacy abstractions
Remove the torchtext dependency

Does your PR introduce any breaking changes? If yes, please list them.

Removes deprecated code

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cc @carmocca @akihironitta @Borda @justusschock @awaelchli @rohitgr7

[codecov]

Codecov Report

Merging #14375 (bdcbaa4) into master (70fe0ed) will decrease coverage by 3%.
The diff coverage is 100%.

❗ Current head bdcbaa4 differs from pull request most recent head ac3525c. Consider uploading reports for the commit ac3525c to get more accurate results

@@            Coverage Diff             @@
##           master   #14375      +/-   ##
==========================================
- Coverage      79%      76%      -3%     
==========================================
  Files         111      332     +221     
  Lines        7258    26867   +19609     
==========================================
+ Hits         5740    20407   +14667     
- Misses       1518     6460    +4942