Remove unused constructors and methods in handles

[destogl]

The PR addresses late detection of invalid (nullptr) pointers detection for interfaces. This is done by not allowing to have at all nullptr in handles. Until now, a handle with nullprt could be created, but there is no way to change it to valid pointer, so there is no much use of this functionality.

Some other related things are also addressed:

• remove unused constructors for handles
• remove bool() operator from handles because it is not relevant anymore
• remove execution of linters on testing stage of hardware_interface package (everything is done using pre-commit)

[mergify[bot]]

This pull request is in conflict. Could you fix it @destogl?

[bmagyar]

After rebasing and playing with this locally a bit I noticed how transmission handles are broken by it :/ unfortunately that bit of code specifically relies on the nullptr functionality. I'll try to touch them up on this PR so that they allow nullptr and those operations still on those specific handles (they inherit it ATM)

[mergify[bot]]

This pull request is in conflict. Could you fix it @destogl?

[mergify[bot]]

This pull request is in conflict. Could you fix it @destogl?