cases: remove old incremental case system

We now run incremental tests with `tools/incr-check.zig` (with the
actual cases being in `test/incremental/`).

Author: mlugg

test/compile_errors.zig

@@ -4,8 +4,7 @@ const Cases = @import("src/Cases.zig");
 
 pub fn addCases(ctx: *Cases, b: *std.Build) !void {
     {
-        const case = ctx.obj("multiline error messages", b.graph.host);
-
+        const case = ctx.obj("multiline error message", b.graph.host);
         case.addError(
             \\comptime {
             \\    @compileError("hello\nworld");
@@ -14,7 +13,10 @@ pub fn addCases(ctx: *Cases, b: *std.Build) !void {
             \\:2:5: error: hello
             \\             world
         });
+    }
 
+    {
+        const case = ctx.obj("multiline error message with trailing newline", b.graph.host);
         case.addError(
             \\comptime {
             \\    @compileError(

test/nvptx.zig

@@ -91,9 +91,10 @@ fn addPtx(ctx: *Cases, target: std.Build.ResolvedTarget, name: []const u8) *Case
     ctx.cases.append(.{
         .name = name,
         .target = target,
-        .updates = std.ArrayList(Cases.Update).init(ctx.cases.allocator),
+        .files = .init(ctx.arena),
+        .case = null,
         .output_mode = .Obj,
-        .deps = std.ArrayList(Cases.DepModule).init(ctx.cases.allocator),
+        .deps = .init(ctx.arena),
         .link_libc = false,
         .emit_bin = false,
         .backend = .llvm,