Revert "Add group_measurements_by_instance_label flag to perfmon configuration (#8688)"

[jsoriano]

Windows tests are failing, Windows builds were not run on original PR (#8688).

This reverts commit fbee6a2.

[jsoriano]

Failing test in jenkins is not related.

[andrewkroh]

I tried to fix the test, but the code isn't behaving as described in the documentation or the test case. The test case that's failing says that it should group everything into a single event but it's actually producing two events (so some grouping is working).

--- PASS: TestGroupByInstance (1.02s)
    pdh_integration_windows_test.go:378: {
          "processor": {
            "name": "_Total",
            "time": {
              "idle": {
                "average": {
                  "ns": 10932693.47826087
                }
              },
              "pct": 0
            }
          }
        }
    pdh_integration_windows_test.go:378: {
          "disk": {
            "bytes": {
              "read": {
                "total": 0
              }
            }
          }
        }