Remove tests of electric-pair-mode and CC-based modes

Remove tests of electric-pair-mode and CC-based modes

The behaviour previously observed in cc-mode-based-modes (and every
other major-mode) when electric-pair-mode or electric-layout-mode is
turned on may no longer be observed: this because CC-mode goes around
the generic implementation of electric-pair-mode.

An alternative is to bind every delimiter key like '{', '}', etc to
'self-insert-command, like most major modes already do, at the cost of
losing c-auto-newline functionality (which was incompatible anyway
before the recent changes of bug#33794).

* test/lisp/electric-tests.el
(electric-pair-test-for): No longer set it.
(define-electric-pair-test): Use js-mode instead of c++ mode,
which broke recently.
(whitespace-chomping-2): Add failing C++ test explicitly.
(electric-layout-int-main-kernel-style): Use plainer-c-mode.
(electric-layout-int-main-allman-style): Deleted.
(electric-modes-int-main-allman-style): Renamed from
electric-layout-int-main-allman-style.