more updates to make sktime 0.7.0 compatible. Disabled ensemble/blend for now

[ngupta23]

Related Issuse or bug

Fixes: #1369

Describe the changes you've made

• Disabled Ensemble / Blending (@TremaMiguel) to have a look at this
• Fixed splitters
• Fixed reduced regression models

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, local variables)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Old unit tests are passing as expected (except blend tests which have been disabled for now)

Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.
• Any dependent changes have been merged and published in downstream modules.

[Yard1]

Looks good. Will wait for @TremaMiguel