Remove references to 32-bit Windows from the user guide (#19297)
Closes #19222
### Summary of the issue:
The user guide makes references to running NVDA on 32-bit Windows.
### Description of user facing changes:
The user guide no longer makes such references.
### Description of developer facing changes:
None
### Description of development approach:
Searched the user guide for 32 and 86. Updated contents as appropriate.
Installed MSSP x64 and ensured that it works with 64-bit NVDA.
### Testing strategy:
Build user guide, check for obvious errors.
### Known issues with pull request:
None
