Disable enhancement feature 7444

Existing issues:

http://d.puremagic.com/issues/show_bug.cgi?id=11276
To enforce slice + assign syntax `a[] = b[]` may cause problems with generic code.

http://d.puremagic.com/issues/show_bug.cgi?id=11244
A case yet difficult to make it clear - combination with operator overloading.
Merge pull request #2673 from 9rnsr/rev7444

[REG2.063] Disable enhancement feature 7444