WyC: Removed Implicit Coercions from Tests #418

Working through valid test cases and eliminating any use of implicit
coercions.  As a result, there are some test cases which no longer make
sense.  There are also some test cases for which we need to figure out
what the right option is.
Merge branch 'feature/418-coercions' of github.com:DavePearce/Whiley into feature/418-coercions

Conflicts:
	tests/valid/RealDiv_Valid_3.whiley