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').
Auxiliary::Web: fixed the previous confidence fix
Revert "Merge pull request #1534 from tasos-r7/bugfix/web-vuln-confidence"

This reverts commit 3840ddccbce47cacb33415ad8301a4cf04fa7462, reversing
changes made to e1891f08366c459701a13f545a13ce5b926e89f6.
Fixing merge conflicts
Merge branch 'bugfix/web-vuln-confidence' of github-r7:tasos-r7/metasploit-framework into bugfix/web-vuln-confidence
Merge pull request #1535 from tasos-r7/bugfix/web-vuln-confidence

Auxiliary::Web: fixed vuln confidence calculation/storage
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.