submodules: update clippy from 29bf75cd to 1df5766c

Fixes clippy toolstate.

Changes:
````
Remove -preview suffix from README
rustup clippy build with latest rustc (breakage due to https://github.com/rust-lang/rust/commit/08f8faedd0e30f45762afbb8d4873f7041e7462c )
Forgot to remove some debugging code ...
Improved code noted by clippy.
Fix bug in `implicit_return`. Bug was already covered by test, but test was not checked for.
fix #3482 and add ui test for it
Don't change current working directory of cargo tests
Use cargo's "PROFILE" envvar and set CLIPPY_DOGFOOD
Use dogfood_runner for deterministic test ordering
Remove unnecessary documentation
Fix dogfood tests.
Added additional reasoning to `Why is this bad?`. Added comment to explain usage of MIR.
Renamed to `implicit_return`. Covered all other kinds besides `ExprKind::Lit`. Added check for replacing `break` with `return`.
Appeasing the Test Gods. Seems I'm not smart enough to run the tests locally before committing.
Renamed `forced_return` to `missing_returns`. Better clarification in the docs. Ran `update_lints`.
Added `FORCED_RETURN` lint.
````

1 files changed, 14 insertions, 14 deletions

diff --git a/src/tools/clippy b/src/tools/clippy
-Subproject 29bf75cd3147d4e34a5e70bd167898a8105f7e5
+Subproject 1df5766cbb559aab0ad5c2296d8b768182b5186