Modernize noexcept specifications

[georgthegreat]

As boost::geometry mandates C++14 since 1.75, I assume this can be merged in C++03-incompatible form.

[barendgehrels]

Looks good to me, indeed C++14 syntax is fine now

[barendgehrels]

One thing, @vissarion , is it better to split it into two commits?
One for library code, one for extensions?

[georgthegreat]

I have split the changes into two commits and removed the dtors as requested

[awulkiew]

@georgthegreat Since you removed the unneded destructors would you be willing to make some other related improvements as well or would you prefer to merge this as it is?

The improvements I'm thinking about are:

• the removal of unneeded default constructors or making them = default in case their existance is documentation-related
• replacement of virtual in what() declaration with override

[georgthegreat]

@awulkiew, I am ok with doing this, but I want this PR merged without this change.
Other improvements are definitely out of scope of this PR.

[barendgehrels]

Thanks for splitting it.

[georgthegreat]

Let's merge it.

[vissarion]

Thanks!

[georgthegreat]

@awulkiew, virtual -> override replacement is here:
https://github.com/boostorg/geometry/pull/1198/files