Prevent from importing temporary legacy classes

tools/check/forbidden_strings_in_code.txt

@@ -164,4 +164,8 @@ Formatter\.formatShortFileSize===1
 # android\.text\.TextUtils
 
 ### This is not a rule, but a warning: the number of "enum class" has changed. For Json classes, it is mandatory that they have `@JsonClass(generateAdapter = false)`. If it is ok, change the value in file forbidden_strings_in_code.txt
-enum class===72
+enum class===72
+
+### Do not import temporary legacy classes
+import im.vector.matrix.android.internal.legacy.riot===3
+import org.matrix.androidsdk.crypto.data===2