Remove the (64-bit) from the bitcoin-qt help message.
Since removing the Windows 32-bit builds, it is no longer information
that is often useful for troubleshooting. This never worked for other
architectures than x86, and the only 32-bit x86 build left is the Linux
one. Linux users tend to know what architecture they are using.It also accidentally ends up in the bitcoin-qt manpage.
This is a backport of Core PR17503