Delete scripts/README.dump_test_schema

It is mostly redundant now that dependencies of dump_test_schema.pl are
in the cplanfile, moreover it was out of date (MooseX::App:Simple has
since become a dependency of ensembl-test as a whole).

scripts/README.dump_test_schema

-dump_test_schema.pl requires the following modules, which cpanm should
-be capable of installing:
-
-  MooseX::App::Simple
-  DBIx::Class::Schema::Loader
-  SQL::Translator
-
-These have more than a few dependencies!
-
-DBD::mysql is also required but if you're using the EnsEMBL API you
-probably have that already.