Remove auto-labels from issue templates

The bug_report, submit-a-request, and submit-a-design-proposal issue
templates currently auto-apply 'bug' and 'enhancement' labels. This
causes issues to arrive pre-labeled with types that may not be accurate,
making triage harder since the template-applied labels can't be trusted.

Removing auto-labels ensures all type classification happens during
triage, giving the team confidence that labeled issues have been
reviewed.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: "\U0001F41B Bug report"
 about: Report a bug or unexpected behavior while using GitHub CLI
 title: ''
-labels: bug
+labels: ''
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/submit-a-design-proposal.md

@@ -2,7 +2,7 @@
 name: "🎨 Submit a design proposal"
 about: Submit a design to resolve an open issue that has both `needs-design` and `help-wanted` labels
 title: ''
-labels: enhancement
+labels: ''
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/submit-a-request.md

@@ -2,7 +2,7 @@
 name: "⭐ Submit a request"
 about: Surface a feature or problem that you think should be solved
 title: ''
-labels: enhancement
+labels: ''
 assignees: ''
 
 ---