Revert "I found some more passing behavior tests"

This reverts commit 0a9b4d092f.

Hm, these are all passing for me locally. I'll have to do some
troubleshooting to figure out which one(s) are failing on the CI.

test/behavior/usingnamespace.zig

@@ -1,5 +1,4 @@
 const std = @import("std");
-const expect = std.testing.expect;
 
 const A = struct {
     pub const B = bool;
@@ -12,42 +11,3 @@ const C = struct {
 test "basic usingnamespace" {
     try std.testing.expect(C.B == bool);
 }
-
-fn Foo(comptime T: type) type {
-    return struct {
-        usingnamespace T;
-    };
-}
-
-test "usingnamespace inside a generic struct" {
-    const std2 = Foo(std);
-    const testing2 = Foo(std.testing);
-    try std2.testing.expect(true);
-    try testing2.expect(true);
-}
-
-usingnamespace struct {
-    pub const foo = 42;
-};
-
-test "usingnamespace does not redeclare an imported variable" {
-    comptime try std.testing.expect(@This().foo == 42);
-}
-
-usingnamespace @import("usingnamespace/foo.zig");
-test "usingnamespace omits mixing in private functions" {
-    try expect(@This().privateFunction());
-    try expect(!@This().printText());
-}
-fn privateFunction() bool {
-    return true;
-}
-
-test {
-    _ = @import("usingnamespace/import_segregation.zig");
-}
-
-usingnamespace @import("usingnamespace/a.zig");
-test "two files usingnamespace import each other" {
-    try expect(@This().ok());
-}