Use existing "Submit" and "Cancel" messages.

src/www/messages/en.json

@@ -3,7 +3,7 @@
   "about-page-title": "About",
   "auto-connect-dialog-detail": "Unless you disconnect from your Outline server, Outline will automatically connect next time you restart your device.",
   "auto-connect-dialog-title": "Stay protected, always",
-  "cancel": "cancel",
+  "cancel": "Cancel",
   "change-language-page-title": "Change Language",
   "close": "Close",
   "connect-button-label": "Connect",
@@ -109,7 +109,6 @@
   "submit": "Submit",
   "submitting": "Submitting...",
   "support-form-access-key-source": "Where did you get your access key?",
-  "support-form-cancel": "Cancel",
   "support-form-cloud-provider-aws": "Amazon Web Services",
   "support-form-cloud-provider-digitalocean": "DigitalOcean",
   "support-form-cloud-provider-gcloud": "Google Cloud",
@@ -120,7 +119,6 @@
   "support-form-email": "Email",
   "support-form-required-field": "Required field",
   "support-form-subject": "Subject",
-  "support-form-submit": "Submit",
   "terms": "Terms",
   "tips": "Tips",
   "undo-button-label": "Undo",

src/www/views/contact_view/support_form/index.ts

@@ -239,14 +239,10 @@ export class SupportForm extends LitElement {
           <p>* = ${this.localize('support-form-required-field')}</p>
 
           <span slot="card-actions">
-            <mwc-button
-              .label=${this.localize('support-form-cancel')}
-              .disabled=${this.disabled}
-              @click=${this.cancel}
-            ></mwc-button>
+            <mwc-button .label=${this.localize('cancel')} .disabled=${this.disabled} @click=${this.cancel}></mwc-button>
             <mwc-button
               type="submit"
-              .label=${this.localize('support-form-submit')}
+              .label=${this.localize('submit')}
               .disabled=${!this.valid || this.disabled}
               @click=${this.submit}
             ></mwc-button>