refactor(windows): remove wm_keyman_keydown and wm_keyman_keyup

[mcdurdin]

Also cleanup the use of state.msg as that had no relevant data in it.

Fixes: #11917

User Testing

• TEST_WINDOWS: Please run a basic test of Windows functionality, verifying that Keyman operates as expected.

[keymanapp-test-bot]

User Test Results

Test specification and instructions

• ✅ TEST_WINDOWS (PASSED): I tested this issue with the attached "keyman-18.0.67-alpha-test-11920" build on the Windows 10 & 11 OS environment: Here is my observation. (notes)

Test Artifacts

• Windows
  • Keyman for Windows
  • FirstVoices Keyboards for Windows
  • Text Editor (32 bit)
  • Text Editor (64 bit)

[rc-swag]

lgtm

[dinakaranr]

Test Results

• TEST_WINDOWS (passed): I tested this issue with the attached "keyman-18.0.67-alpha-test-11920" build on the Windows 10 & 11 OS environment: Here is my observation.

1. Installed the "keyman-18.0.67.exe" file.
2. Keyman keyboard added in the system tray.
3. Open the keyman "Configuration" window.
4. Installed and uninstalled keyboards on the "Keyboard Layouts" tab.
5. Hotkeys works which is mentioned on the "Hotkeys" tab.
6. Keyboard switched between languages by (Left-ALT + Shift)
7. The keyboard works well in Notepad and libreoffice.
   The feature works well in Windows 10 & 11 OS environments. Thank you.

[keyman-server]

Changes in this pull request will be available for download in Keyman version 18.0.68-alpha