System.Configuration.ConfigurationManager.Tests: use Assembly.Location to determine ThisApplicationPath. (#112231)

* System.Configuration.ConfigurationManager.Tests: use Assembly.Location to determine ThisApplicationPath.

* Remove exePath_UserLevelNone test.

This is functionally covered other tests (OpenExeConfiguration2 and OpenExeConfiguration2_ExePath_DoesNotExist)
that do not rely on the test deployment.

Author: tmds

src/libraries/System.Configuration.ConfigurationManager/tests/Mono/ConfigurationManagerTest.cs

@@ -131,15 +131,6 @@ public void OpenExeConfiguration2_ExePath_DoesNotExist()
             }
         }
 
-        [Fact]
-        [ActiveIssue("https://github.com/dotnet/runtime/issues/21319", TargetFrameworkMonikers.NetFramework)]
-        public void exePath_UserLevelNone()
-        {
-            string name = TestUtil.ThisApplicationPath;
-            SysConfig config = ConfigurationManager.OpenExeConfiguration(name);
-            Assert.Equal(TestUtil.ThisApplicationPath + ".config", config.FilePath);
-        }
-
         [Fact]
         public void exePath_UserLevelPerRoaming()
         {

src/libraries/System.Configuration.ConfigurationManager/tests/Mono/TestUtil.cs

@@ -54,15 +54,6 @@ public static void RunWithTempFiles(MyAction<string, string> action)
             }
         }
 
-        public static string ThisApplicationPath
-        {
-            get
-            {
-                return Path.Combine(AppDomain.CurrentDomain.BaseDirectory,
-                    Assembly.GetEntryAssembly().ManifestModule.Name);
-            }
-        }
-
         public static string ThisConfigFileName
         {
             get