Investigate changes in SERVER-54504: Disable taskExecutorPoolSize for Linux

The taskExecutorPoolSize server parameter will no longer be used on linux as it will be set to its default value of 1. The parameter is still available for Windows and Mac.

Description of Linked Ticket

This option is not useful for linux machines running 4.2 and beyond (and can cause problems if changed past the default of 1). So, we must disable this option for linux machines (It is always a value of 1). 

This parameter will still be available for Windows & OS X since we have found that it is useful for those machines, and that there are a non-trivial number of clusters running Windows in production.

Acceptance Criteria:

Customers can no longer change this parameter on linux machines.