remove date parse callback from wufb resource

Summary:
Who would have thought there would be an actual value in this registry key?
Basically if there is a value in `HKLM:\Software\Policies\Microsoft\Windows\WindowsUpdate\PauseFeatureUpdatesStartTime` the resource will try to validate the date and fail if it doesn't match expectations, e.g.:
```
PS > Get-ItemProperty HKLM:\Software\Policies\Microsoft\Windows\WindowsUpdate -Name PauseFeatureUpdatesStartTime

PauseFeatureUpdatesStartTime : 0

PS > soloctl -icH
...
Recipe: cpe_windows_update_for_business::default
  * cpe_windows_update_for_business[Configure Windows Update for Business] action config

    ================================================================================
    Error executing action `config` on resource 'cpe_windows_update_for_business[Configure Windows Update for Business]'
    ================================================================================

    Date::Error
    -----------
    invalid date
```

We're still trying to mitigate CVE-2024-38063 so at this point the explicit `nil` value in the custom resource means this will clear whatever value is there. Since we want folks to update as soon as possible this may be more preferable behavior. Once we're out of the danger zone we can revisit validating this setting.

Differential Revision: D61515598

fbshipit-source-id: 9fdfaf79851bd186723cd5ed17cd58e4d139500d

itchef/cookbooks/cpe_windows_update_for_business/resources/cpe_windows_update_for_business.rb

@@ -61,22 +61,12 @@
 
 property :pause_quality_updates_start_time,
          [String, NilClass],
-         :callbacks => {
-           'is not in yyyy-mm-dd format' => lambda { |v|
-             DateTime.parse(v).strftime('%Y-%m-%d') == v
-           },
-         },
          :default => lazy {
                        node['cpe_windows_update_for_business']['pause_quality_updates_start_time']
                      }
 
 property :pause_feature_updates_start_time,
          [String, NilClass],
-         :callbacks => {
-           'is not in yyyy-mm-dd format' => lambda { |v|
-             DateTime.parse(v).strftime('%Y-%m-%d') == v
-           },
-         },
          :default => lazy {
                        node['cpe_windows_update_for_business']['pause_feature_updates_start_time']
                      }