Removing some duplicated code.

Self explained.

tests/robot/metrics_test.robot

@@ -8,19 +8,16 @@ ${TOKEN}    Token ${API_TOKEN}
 
 *** Test Cases ***
 
-TC03 Check Metrics Page
-    ${auth}=  Evaluate  ("${USER_API}", "${PASSWORD_API}")
-    &{HEADERS}    Create Dictionary    Authorization=${TOKEN} Content-Type=${CONTENT_TYPE}
-    Create Session    robot_test_session    ${BASE_URL}    headers=${HEADERS} 
-    ${response}=    GET On session    robot_test_session    /${PAGE}    headers=${HEADERS}    auth=${auth}    expected_status=200
+Check Metrics Page
+    ${response}=    GET    ${BASE_URL}/metrics    expected_status=200
     Log to console    ${\n}
-    Check metrics response status "${response.ok}" "${PAGE}"
+    Check metrics response status "${response.ok}" "metrics"
     Log to console    ${\n}
 
-TC03.1 Check Nonexistent Page
-    ${auth}=  Evaluate  ("${USER_API}", "${PASSWORD_API}")
-    &{HEADERS}    Create Dictionary    Authorization=${TOKEN} Content-Type=${CONTENT_TYPE}
-    ${response}=    GET On session    robot_test_session    /api/plugins/nonexistent_plugin    auth=${auth}    headers=${HEADERS}    expected_status=404
+Check Nonexistent Page
+    ${HEADERS}       Create Dictionary    Content-Type    application/json    Authorization    ${TOKEN} 
+    Log to console    ${\n}
+    ${response}=    GET    ${BASE_URL}/nonexisting_page    headers=${HEADERS}  expected_status=404
     Log to console    ${\n}
     Check metrics response status "${response.ok}" "nonexistent"
     Log to console    ${\n}
@@ -34,4 +31,4 @@ Check metrics response status "${response.ok}" "${PAGE}"
     ELSE
         Log to console    ${\n}${PAGE} Not Ready
         Log    ${\n}${PAGE} Not Ready
-    END
\ No newline at end of file
+    END