Remove incremental test, disable incremental for cargo tests (#14910)

Fixes https://github.com/rust-lang/rust-clippy/issues/11126

It avoids the ICE when the number of lints changes, this is only a
problem for clippy in development but cleaning the clippy dir requires a
lot of rebuilding

changelog: none

tests/compile-test.rs

@@ -273,10 +273,10 @@ fn run_ui_cargo(cx: &TestContext) {
     config.program.input_file_flag = CommandBuilder::cargo().input_file_flag;
     config.program.out_dir_flag = CommandBuilder::cargo().out_dir_flag;
     config.program.args = vec!["clippy".into(), "--color".into(), "never".into(), "--quiet".into()];
-    config
-        .program
-        .envs
-        .push(("RUSTFLAGS".into(), Some("-Dwarnings".into())));
+    config.program.envs.extend([
+        ("RUSTFLAGS".into(), Some("-Dwarnings".into())),
+        ("CARGO_INCREMENTAL".into(), Some("0".into())),
+    ]);
     // We need to do this while we still have a rustc in the `program` field.
     config.fill_host_and_target().unwrap();
     config.program.program.set_file_name(if cfg!(windows) {

tests/ui/to_string_in_format_args_incremental.fixed

@@ -1,11 +0,0 @@
-//@compile-flags: -C incremental=target/debug/test/incr
-
-#![allow(clippy::uninlined_format_args)]
-
-// see https://github.com/rust-lang/rust-clippy/issues/10969
-
-fn main() {
-    let s = "Hello, world!";
-    println!("{}", s);
-    //~^ to_string_in_format_args
-}

tests/ui/to_string_in_format_args_incremental.rs

@@ -1,11 +0,0 @@
-//@compile-flags: -C incremental=target/debug/test/incr
-
-#![allow(clippy::uninlined_format_args)]
-
-// see https://github.com/rust-lang/rust-clippy/issues/10969
-
-fn main() {
-    let s = "Hello, world!";
-    println!("{}", s.to_string());
-    //~^ to_string_in_format_args
-}

tests/ui/to_string_in_format_args_incremental.stderr

@@ -1,11 +0,0 @@
-error: `to_string` applied to a type that implements `Display` in `println!` args
-  --> tests/ui/to_string_in_format_args_incremental.rs:9:21
-   |
-LL |     println!("{}", s.to_string());
-   |                     ^^^^^^^^^^^^ help: remove this
-   |
-   = note: `-D clippy::to-string-in-format-args` implied by `-D warnings`
-   = help: to override `-D warnings` add `#[allow(clippy::to_string_in_format_args)]`
-
-error: aborting due to 1 previous error
-