remove outdated validatesns library and replace with maintainable code

requirements.txt

@@ -10,8 +10,6 @@ amqp==5.1.1
     # via kombu
 arrow==1.2.2
     # via isoduration
-asn1crypto==1.5.1
-    # via oscrypto
 async-timeout==4.0.2
     # via redis
 attrs==21.4.0
@@ -150,6 +148,8 @@ kombu==5.2.4
     # via celery
 lxml==4.9.1
     # via -r requirements.in
+m2crypto==0.38.0
+    # via -r requirements.in
 mako==1.2.0
     # via alembic
 markupsafe==2.1.1
@@ -171,8 +171,6 @@ notifications-utils @ git+https://github.com/GSA/notifications-utils.git
     # via -r requirements.in
 orderedset==2.0.3
     # via notifications-utils
-oscrypto==1.3.0
-    # via validatesns
 packaging==21.3
     # via
     #   bleach
@@ -251,7 +249,6 @@ six==1.16.0
     #   flask-marshmallow
     #   python-dateutil
     #   rfc3339-validator
-    #   validatesns
 smartypants==2.0.1
     # via notifications-utils
 soupsieve==2.3.2.post1
@@ -272,8 +269,6 @@ urllib3==1.26.9
     # via
     #   botocore
     #   requests
-validatesns==0.1.1
-    # via -r requirements.in
 vine==5.0.0
     # via
     #   amqp