various tests: replace BEGIN/require/import by use

[mauke]

That is, turn

BEGIN {
    require Foo;
    Foo->import(...);
}

into

use Foo ...;

(Except for a few tests that did the require Config; Config->import dance without actually using %Config anywhere, so I just deleted the import code.)

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• This set of changes does not require a perldelta entry.

[jkeenan]

I vaguely recall that there was some rationale for the use of BEGIN/require/import in the past (as opposed to use). Does anyone recall what that was?