Remove gds_zendesk gem from dependencies

It's no longer used

Gemfile

@@ -9,7 +9,6 @@ gem "cancancan"
 gem "dartsass-rails"
 gem "gds-api-adapters"
 gem "gds-sso"
-gem "gds_zendesk"
 gem "govuk_admin_template"
 gem "govuk_app_config"
 gem "govuk_publishing_components"

Gemfile.lock

@@ -154,8 +154,6 @@ GEM
     faraday (2.10.0)
       faraday-net_http (>= 2.0, < 3.2)
       logger
-    faraday-multipart (1.0.4)
-      multipart-post (~> 2)
     faraday-net_http (3.1.0)
       net-http
     ffi (1.17.0-aarch64-linux-gnu)
@@ -176,9 +174,6 @@ GEM
       rails (>= 7)
       warden (~> 1.2)
       warden-oauth2 (~> 0.0.1)
-    gds_zendesk (3.7.0)
-      null_logger (~> 0)
-      zendesk_api (>= 1.37, < 4.0)
     globalid (1.2.1)
       activesupport (>= 6.1)
     google-protobuf (4.27.3-aarch64-linux)
@@ -241,7 +236,6 @@ GEM
       domain_name (~> 0.5)
     i18n (1.14.5)
       concurrent-ruby (~> 1.0)
-    inflection (1.0.0)
     io-console (0.7.2)
     irb (1.14.0)
       rdoc (>= 4.0.0)
@@ -296,7 +290,6 @@ GEM
     msgpack (1.7.2)
     multi_xml (0.7.1)
       bigdecimal (~> 3.1)
-    multipart-post (2.4.1)
     mutex_m (0.2.0)
     net-http (0.4.1)
       uri
@@ -767,13 +760,6 @@ GEM
     xpath (3.2.0)
       nokogiri (~> 1.8)
     zeitwerk (2.6.17)
-    zendesk_api (3.1.0)
-      faraday (> 2.0.0)
-      faraday-multipart
-      hashie (>= 3.5.2, < 6.0.0)
-      inflection
-      mini_mime
-      multipart-post (~> 2.0)
 
 PLATFORMS
   aarch64-linux
@@ -789,7 +775,6 @@ DEPENDENCIES
   factory_bot_rails
   gds-api-adapters
   gds-sso
-  gds_zendesk
   govuk_admin_template
   govuk_app_config
   govuk_publishing_components