Remove Jessica from maintainers list (#10731)

Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>

.github/CODEOWNERS

@@ -4,4 +4,4 @@
 /discovery/kubernetes @brancz
 /tsdb @codesome
 /promql @codesome @roidelapluie
-/cmd/promtool @jessicagreben @dgl
+/cmd/promtool @dgl

MAINTAINERS.md

@@ -3,7 +3,7 @@
 Julien Pivotto (<roidelapluie@prometheus.io> / @roidelapluie) and Levi Harrison (<levi@leviharrison.dev> / @LeviHarrison) are the main/default maintainers, some parts of the codebase have other maintainers:
 
 * `cmd`
-  * `promtool`: David Leadbeater (<dgl@dgl.cx> / @dgl), Jessica Grebenschikov (<jessicagreben@prometheus.io> / @jessicagreben)
+  * `promtool`: David Leadbeater (<dgl@dgl.cx> / @dgl)
 * `discovery`
   * `k8s`: Frederic Branczyk (<fbranczyk@gmail.com> / @brancz)
 * `documentation`