Function: removeprimes
Section: number_theoretical
C-Name: removeprimes
Prototype: DG
Help: removeprimes({x=[]}): remove primes in the vector x from the prime table.
 x can also be a single integer. List the current extra primes if x is omitted.
Doc: removes the primes listed in $x$ from
 the prime number table. In particular \kbd{removeprimes(addprimes())} empties
 the extra prime table. $x$ can also be a single integer. List the current
 extra primes if $x$ is omitted.