Remove SAPI4 (#19290)
Closes #18310
Closes #19030
Closes #17964
### Summary of the issue:
SAPI4 is 32-bit only. As we don't currently have a SAPI4 bridge or a
compatibility shim, we need to remove support.
### Description of user facing changes:
SAPI4 speech synthesizers are no longer supported by NVDA.
### Description of developer facing changes:
SAPI4 and related code has been removed.
### Description of development approach:
Deleted the synth drivers and related code.
### Testing strategy:
System and usage tests.
Tried changing synthesizers to ensure that things still work as
expected.
### Known issues with pull request:
This may stop some users from using their preferred speech synthesizer.
For many users, this is a luxury, however for some a SAPI4 synth may be
a necessity, due to language, hearing, auditory processing issues etc.
