test: remove old-style incremental cases, add a few new incremental cases

These cases have been disabled for a while, and we have transitioned to
using a compact file format for incremental test cases.

I was originally planning to port all of these cases, but the vast
majority aren't testing anything interesting, so it wasn't worth the
effort. I did look through each one; anything interesting being tested
has been extracted into a new case in `test/incremental/`.

Two of the new tests are currently failing with the self-hosted ELF
linker, and thus are currently only enabled with the C backend.

Resolves: #12844

test/incremental/recursive_function_becomes_non_recursive

@@ -0,0 +1,28 @@
+//#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+#update=initial version
+#file=main.zig
+pub fn main() !void {
+    try foo(false);
+}
+fn foo(recurse: bool) !void {
+    const stdout = std.io.getStdOut().writer();
+    if (recurse) return foo(true);
+    try stdout.writeAll("non-recursive path\n");
+}
+const std = @import("std");
+#expect_stdout="non-recursive path\n"
+
+#update=eliminate recursion and change argument
+#file=main.zig
+pub fn main() !void {
+    try foo(true);
+}
+fn foo(recurse: bool) !void {
+    const stdout = std.io.getStdOut().writer();
+    if (recurse) return stdout.writeAll("x==1\n");
+    try stdout.writeAll("non-recursive path\n");
+}
+const std = @import("std");
+#expect_stdout="x==1\n"