Issue forms: remove unused assignee tag

Signed-off-by: Ekaterina Gerasimova <kittykat3756@gmail.com>

.github/ISSUE_TEMPLATE/bug-desktop.yml

@@ -1,8 +1,6 @@
 name: Bug report for the Element desktop app (not in a browser)
 description: File a bug report if you are using the desktop Element application.
 labels: [T-Defect]
-assignees:
-  -   
 body:
   - type: markdown
     attributes:

.github/ISSUE_TEMPLATE/bug-web.yml

@@ -1,8 +1,6 @@
 name: Bug report for Element Web (in browser)
 description: File a bug report if you are using Element in a web browser like Firefox, Chrome, Edge, and so on.
 labels: [T-Defect]
-assignees:
-  -   
 body:
   - type: markdown
     attributes: