This diff removes 4 unused ARMv7 NEON fixed-point DSP functions.

The function were originally moved here by 4958f35a (Dec 2013).

After 9e05421d (Jan 2021), as part of the refactor of the AC3
DSP to consistently use 32-bit sample format in the encoder, these
functions were removed from the DSP function table, but the ARMv7
implementations were kept.
Signed-off-by: Geoff Hill <geoff@geoffhill.org>