Revert "fix: dde-file-manager crash"

[Johnson-zs]

This reverts commit 9f162cb.

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 移除了FileManagerWindowsManager::instance().windowIdList().count() <= 0的检查，需要确认这一改动是否符合预期逻辑。
• 移除了与QApplication的连接和断开信号的代码，需要确认这是否是预期的行为。
• 删除了widgets/filemanagerwindowsmanager.h的引用，如果这个头文件不再被使用，那么这是一个好的改动。

是否建议立即修改:

• 是，需要确认移除FileManagerWindowsManager相关代码是否会影响功能，并且确认与QApplication的连接和断开信号的改动是否正确。

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Johnson-zs, max-lvs

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• debian/deepin/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment