migration: Drop unused VMSTATE_FLOAT64 support

migration: Drop unused VMSTATE_FLOAT64 support

Commit ef96e3ae9698d6 in January 2019 removed the last user of the
VMSTATE_FLOAT64* macros. These were used by targets which defined
their floating point register file as an array of 'float64'.

We used to try to maintain a stricter distinction between
'float64' (a type for holding an integer representing an IEEE float)
and 'uint64_t', including having a debug option for 'float64' being
a struct and supposedly mandatory macros for converting between
float64 and uint64_t. We no longer think that's a usefully
strong distinction to draw and we allow ourselves to freely
assume that float64 really is just a 64-bit integer type, so
for new targets we would simply recommend use of the uint64_t type
for a floating point register file. The float64 type remains
as a useful way of documenting in the type signature of helper
functions and the like that they expect to receive an IEEE float
from the TCG generated code rather than an arbitrary integer.

Since the VMSTATE_FLOAT64* macros have no remaining users and
we don't recommend new code uses them, delete them.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20201022120830.5938-1-peter.maydell@linaro.org>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>