doc: remove labels from issue templates (#1280)

Author: knakad

.github/ISSUE_TEMPLATE/bug_report.md

@@ -2,7 +2,7 @@
 name: Bug report
 about: File a report to help us reproduce and fix the problem
 title: ''
-labels: 'bug'
+labels: ''
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/documentation-request.md

@@ -2,7 +2,7 @@
 name: Documentation request
 about: Request improved documentation
 title: ''
-labels: 'doc update'
+labels: ''
 assignees: ''
 
 ---

.github/ISSUE_TEMPLATE/feature_request.md

@@ -2,7 +2,7 @@
 name: Feature request
 about: Suggest an improvement for this library
 title: ''
-labels: 'feature request'
+labels: ''
 assignees: ''
 
 ---