Remove the unused failing allocator from the terminal store tests

The only test that used it was removed when fx started loading shell
startup files once per process, and the allocator stayed behind with no
callers.

src/core/terminal/store.zig

@@ -6119,83 +6119,6 @@ const TestStoreFixture = struct {
     }
 };
 
-const OneShotFailingAllocator = struct {
-    failing: std.testing.FailingAllocator,
-
-    fn init(alloc: Allocator) OneShotFailingAllocator {
-        return .{ .failing = .init(alloc, .{}) };
-    }
-
-    fn allocator(self: *OneShotFailingAllocator) Allocator {
-        return .{ .ptr = self, .vtable = &.{
-            .alloc = allocate,
-            .resize = resize,
-            .remap = remap,
-            .free = free,
-        } };
-    }
-
-    fn allocate(
-        raw: *anyopaque,
-        len: usize,
-        alignment: std.mem.Alignment,
-        return_address: usize,
-    ) ?[*]u8 {
-        const self: *OneShotFailingAllocator = @ptrCast(@alignCast(raw));
-        const result = self.failing.allocator().rawAlloc(
-            len,
-            alignment,
-            return_address,
-        );
-        if (result == null and self.failing.has_induced_failure) {
-            self.failing.fail_index = std.math.maxInt(usize);
-        }
-        return result;
-    }
-
-    fn resize(
-        raw: *anyopaque,
-        memory: []u8,
-        alignment: std.mem.Alignment,
-        new_len: usize,
-        return_address: usize,
-    ) bool {
-        const self: *OneShotFailingAllocator = @ptrCast(@alignCast(raw));
-        return self.failing.allocator().rawResize(
-            memory,
-            alignment,
-            new_len,
-            return_address,
-        );
-    }
-
-    fn remap(
-        raw: *anyopaque,
-        memory: []u8,
-        alignment: std.mem.Alignment,
-        new_len: usize,
-        return_address: usize,
-    ) ?[*]u8 {
-        const self: *OneShotFailingAllocator = @ptrCast(@alignCast(raw));
-        return self.failing.allocator().rawRemap(
-            memory,
-            alignment,
-            new_len,
-            return_address,
-        );
-    }
-
-    fn free(
-        raw: *anyopaque,
-        memory: []u8,
-        alignment: std.mem.Alignment,
-        return_address: usize,
-    ) void {
-        const self: *OneShotFailingAllocator = @ptrCast(@alignCast(raw));
-        self.failing.allocator().rawFree(memory, alignment, return_address);
-    }
-};
-
 const ConcurrentAppend = struct {
     session: *DurableSession,
     result: ?anyerror = null,