--mcmc-noinit option doesn't work

[ndokmai]

Currently, the --mcmc-noinit option doesn't cause any changes in the program. This is due to the following line

https://github.com/odelaneau/shapeit5/blob/3d97fcd0173066d723db07c5a0b7f3153450cc34/phase_common/src/phaser/phaser_initialise.cpp#L106

that should be changed to options.count("mcmc-noinit").