MediaService: Remove allowedMimeType application/pdf

Uploading PDFs does not work with imgur and therefore HedgeDoc should not offer that.

See #533

Signed-off-by: Philip Molares <philip.molares@udo.edu>

docs/content/dev/public_api.yml

@@ -496,10 +496,6 @@ paths:
         required: true
         description: The binary file to upload.
         content:
-          application/pdf:
-            schema:
-              type: string
-              format: binary
           image/apng:
             schema:
               type: string

src/media/media.service.ts

@@ -47,7 +47,6 @@ export class MediaService {
 
   private static isAllowedMimeType(mimeType: string): boolean {
     const allowedTypes = [
-      'application/pdf',
       'image/apng',
       'image/bmp',
       'image/gif',