Remove uses of Test::Deep from test suite.

This is my first PR in the interest of making Path::Tiny tinier.

Two test files load Test::Deep but do not use it; these were trivial to eliminate.

In two other test files, Test::Deep can be easily replaced with `is_deeply` from Test::More.

Test::Deep itself has non-core dependencies - it depends on Test::NoWarnings, which depends on Test::Tester. So this cuts out more than one dependency.