Use migrations from metasploit_data_models

[#44034071]

metasploit_data_models version 0.5.0 copied the migrations from
metasploit-framework/data/sql/migrate to
metasploit_data_models/db/migrate so that specs could be written the Mdm
models in metasploit_data_models.  As part of the specs, :null => false
columns that should be :null => true were discovered, so a new migration
was added, but to metasploit_data_models/db/migrate, so it could be
tested.  Instead of replicating migrations back and forth, I'm removing
the migrations completely from metasploit-framework and changing the
default migration path in Msf::DbManager#migration_paths to
MetasploitDataModels.root.join('db', 'migrate').
Update to master tag of 0.5.1 of metasploit_data_models

[#44034071]
Add metasploit_data_models 0.5.1 to gemcache

[#44034071]
Merge pull request #1533 from rapid7/feature/migrations-in-metasploit_data_models

All steps passing as described.