chore: remove remove-unnecessary-files

removes document text files that are no longer needed by #9541.

src/docs/manual_let_else.txt

@@ -1,20 +0,0 @@
-### What it does
-
-Warn of cases where `let...else` could be used
-
-### Why is this bad?
-
-`let...else` provides a standard construct for this pattern
-that people can easily recognize. It's also more compact.
-
-### Example
-
-```
-let v = if let Some(v) = w { v } else { return };
-```
-
-Could be written:
-
-```
-let Some(v) = w else { return };
-```

src/docs/seek_to_start_instead_of_rewind.txt

@@ -1,22 +0,0 @@
-### What it does
-
-Checks for jumps to the start of a stream that implements `Seek`
-and uses the `seek` method providing `Start` as parameter.
-
-### Why is this bad?
-
-Readability. There is a specific method that was implemented for
-this exact scenario.
-
-### Example
-```
-fn foo<T: io::Seek>(t: &mut T) {
-    t.seek(io::SeekFrom::Start(0));
-}
-```
-Use instead:
-```
-fn foo<T: io::Seek>(t: &mut T) {
-    t.rewind();
-}
-```