disable building of lalstochastic by default

lalstochastic hasn't been used for a long time, this is the first step
in removing the code. the steps to remove this will be:

1) disable the code from building by default (this commit).
2) remove the ability to build the codes at all.
3) remove the code itself.

this is going to be done in these steps to make getting the codes back
easier, the build system will change therefore if the codes are removed
in the same commit as updating the build system to not build them it
will be harded to revert if the codes are ever needed again.
12 jobs for disable_stochastic in 24 minutes and 56 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Level0
passed #23906
level0:lal

00:02:44

 
  Level1
passed #23907
level1:lalframe

00:01:23

passed #23908
level1:lalmetaio

00:01:22

passed #23909
level1:lalsimulation

00:05:04

passed #23910
level1:lalxml

00:01:11

 
  Level2
passed #23911
level2:lalburst

00:01:35

passed #23912
level2:lalinspiral

00:05:03

passed #23913
level2:lalpulsar

00:03:15

passed #23914
level2:lalstochastic

00:01:30

 
  Level3
passed #23915
level3:laldetchar

00:01:45

passed #23916
level3:lalinference

00:06:28

 
  Level4
passed #23917
level4:lalapps

00:05:34