…026.2 as it is not stable enough yet. (#20206)

Fixes #19667
Fixes #19819
Reverts #19672
Summary of the issue:

Experimental code was recently added to NVDA (after 2026.1) that caused the 32 bit synthDriver shim to send its audio back to NvDA for playing, rather than playing it directly in its own process. This was done to test / prepare for the time when add-ons would be running in an app container, and therefore probably would not have direct access to the audio device.
However, currently this code is still quite unstable, causing NVDA to freeze when rapidly changing the speech rate, or arrowing up and down in lists, when using sapi4 or 32 bit sapi5.
This instability is most likely a similar issue to what was fixed in pr #19609, where RPYC is handoing the return of a call on the wrong thread. But in this case, it is calls to/from nvwave in NVDA's process.
Description of user facing changes:
Description of developer facing changes:
Description of development approach:

    Simply instruct the synthDriver process not to install the nvwave proxy that brokers back to NvDA.
    Reverts Re-enable audio ducking for proxied x86 speech synths #19672 so that 32 bit synthDrivers suspend audioDucking while they are running, as audioDucking cnanot be supported without brokering audio.