Fix usage of strict/warnings in Compiler::Lexer::Constants

This patch:
- puts a single `use strict; use warnings;` at the top of the file and removes all instances in each package.
- removes every `1;` line except the last of the file.

Because:
* `use strict` and `use warnings` are lexical. `package` doesn't define a new lexical scope. So using `use strict; use warnings;` just once at the top of the file is enough: it will apply to the whole compilation unit, not just to the first package.
* In a similar way the true value (usually `1;`) required at the end of a module only applies to the last statement of the *file*, not as the last statement of a package (because such a thing doesn't exist anyway).