Remove a couple unnecessary ToStrings in System.DirectoryServices (#3…

…4244)

These are calling ToString on a StringBuilder, but StringBuilder.Append has a StringBuilder-based overload in netcoreapp.  On other builds this will just fall back to the object-based overload, which will call ToString.

src/libraries/System.DirectoryServices.AccountManagement/src/System/DirectoryServices/AccountManagement/AD/ADStoreCtx_LoadStore.cs

@@ -630,7 +630,7 @@ private Principal FindPrincipalByIdentRefHelper(
 
                     innerLdapFilter.Append(')');
 
-                    ldapFilter.Append(innerLdapFilter.ToString());
+                    ldapFilter.Append(innerLdapFilter);
                 }
 
                 // Wrap off the filter

src/libraries/System.DirectoryServices/src/Interop/AdsValueHelper2.cs

@@ -153,7 +153,7 @@ public object GetValue()
                         strb.Append("B:");
                         strb.Append(binaryPart.Length);
                         strb.Append(':');
-                        strb.Append(binaryPart.ToString());
+                        strb.Append(binaryPart);
                         strb.Append(':');
                         strb.Append(Marshal.PtrToStringUni(dnb.pszDNString));