random: Drop fake entropy gathering function.

* random/random-csprng.c (faked_rng): Drop variable.
(gather_faked): Drop prototype and function.
(initialize): Drop fallback code.
(_gcry_rngcsprng_is_faked): Change accordingly.

The fake entropy gathering function is deemed too dangerous to be
used by accident, and is therefore removed.

This reverts commit 468a5796ffb1a7776db4004d534376c1b981d740.

• Signed-off-by: Justus Winter <justus@g10code.com>