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/function_becomes_inline

@@ -0,0 +1,35 @@
+//#target=x86_64-linux-selfhosted
+#target=x86_64-linux-cbe
+#target=x86_64-windows-cbe
+#update=non-inline version
+#file=main.zig
+pub fn main() !void {
+    try foo();
+}
+fn foo() !void {
+    try std.io.getStdOut().writer().writeAll("Hello, World!\n");
+}
+const std = @import("std");
+#expect_stdout="Hello, World!\n"
+
+#update=make function inline
+#file=main.zig
+pub fn main() !void {
+    try foo();
+}
+inline fn foo() !void {
+    try std.io.getStdOut().writer().writeAll("Hello, World!\n");
+}
+const std = @import("std");
+#expect_stdout="Hello, World!\n"
+
+#update=change string
+#file=main.zig
+pub fn main() !void {
+    try foo();
+}
+inline fn foo() !void {
+    try std.io.getStdOut().writer().writeAll("Hello, `inline` World!\n");
+}
+const std = @import("std");
+#expect_stdout="Hello, `inline` World!\n"