gems: drop webmock.

Gemfile.lock

@@ -123,8 +123,6 @@ GEM
     coderay (1.1.3)
     concurrent-ruby (1.1.6)
     connection_pool (2.2.3)
-    crack (0.4.3)
-      safe_yaml (~> 1.0.0)
     crass (1.0.6)
     daemons (1.3.1)
     delayed_job (4.1.8)
@@ -156,7 +154,6 @@ GEM
       ffi (~> 1.0)
     globalid (0.4.2)
       activesupport (>= 4.2.0)
-    hashdiff (1.0.1)
     http (4.4.1)
       addressable (~> 2.3)
       http-cookie (~> 1.0)
@@ -402,10 +399,6 @@ GEM
     unicorn-worker-killer (0.4.4)
       get_process_mem (~> 0)
       unicorn (>= 4, < 6)
-    webmock (3.8.3)
-      addressable (>= 2.3.6)
-      crack (>= 0.3.2)
-      hashdiff (>= 0.4.0, < 2.0.0)
     webpacker (5.1.1)
       activesupport (>= 5.2)
       rack-proxy (>= 0.6.1)
@@ -497,7 +490,6 @@ DEPENDENCIES
   stripe
   unicorn
   unicorn-worker-killer
-  webmock
   webpacker (>= 4.0.x)
   whenever