Remove useless goto/label statements

[PetroZarytskyi]

This PR removes all pairs of goto/label statements with nothing in between:

goto _label0;
_label0:

Obviously, this bit of code doesn't do anything. Such cases make up the majority of goto uses in Clad. The idea in this PR is to check whether the corresponding return statement is the last statement in the function's body. If it is, there's no need to create a goto statement. Before this PR, Clad tests contained 328 goto stmts, now they only contain 21.

Fixes #526.

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 93.75%. Comparing base (4ebd1af) to head (d61d0a4).

Additional details and impacted files

[](https://app.codecov.io/gh/vgvassilev/clad/pull/938?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vassil+Vassilev) ```diff @@ Coverage Diff @@ ## master #938 +/- ## ========================================== - Coverage 93.76% 93.75% -0.01% ========================================== Files 54 54 Lines 7781 7786 +5 ========================================== + Hits 7296 7300 +4 - Misses 485 486 +1 ``` | [Files](https://app.codecov.io/gh/vgvassilev/clad/pull/938?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vassil+Vassilev) | Coverage Δ | | |---|---|---| | [lib/Differentiator/ReverseModeVisitor.cpp](https://app.codecov.io/gh/vgvassilev/clad/pull/938?src=pr&el=tree&filepath=lib%2FDifferentiator%2FReverseModeVisitor.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vassil+Vassilev#diff-bGliL0RpZmZlcmVudGlhdG9yL1JldmVyc2VNb2RlVmlzaXRvci5jcHA=) | `97.26% <91.66%> (-0.04%)` | :arrow_down: | | [Files](https://app.codecov.io/gh/vgvassilev/clad/pull/938?dropdown=coverage&src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vassil+Vassilev) | Coverage Δ | | |---|---|---| | [lib/Differentiator/ReverseModeVisitor.cpp](https://app.codecov.io/gh/vgvassilev/clad/pull/938?src=pr&el=tree&filepath=lib%2FDifferentiator%2FReverseModeVisitor.cpp&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Vassil+Vassilev#diff-bGliL0RpZmZlcmVudGlhdG9yL1JldmVyc2VNb2RlVmlzaXRvci5jcHA=) | `97.26% <91.66%> (-0.04%)` | :arrow_down: |

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"

[github-actions[bot]]

clang-tidy review says "All clean, LGTM! :+1:"