Remove incorrect old paragraph

[jhauser-us]

This paragraph is incorrect and should have been removed in commit c335c26:

The behavior upon accessing vsireg* from M-mode or HS-mode, while vsiselect holds a value that is not implemented at HS level, is UNSPECIFIED. Similarly, the behavior upon accessing sireg* (really vsireg*) from VS-mode, while vsiselect holds a value that is not implemented at VS level, is UNSPECIFIED.

That commit replaces this paragraph, but then incorrectly adds it back again.