Address my r76242 fixme.

Address my r76242 fixme.
Remove invalidateTitleProtectionCache().
Set $mTitleProtection to the proper value when we change it instead of forcing a reload via the protected_titles table.
Make Title::loadRestrictionsFromRows() private since it is only called by the private loadRestrictionsFromResultWrapper() and nobody should be fiddling with such title internals anyway	 (follow up to r54527).
Removed the invalidateTitleProtectionCache() from getCascadeProtectionSources() since that function only deals with titles which do exist. There's nothing to invalidate there.