std::remove with vector::erase and undefined behavior

24.2.1/7 Most of the library’s algorithmic templates that operate on data structures have interfaces that use ranges. A range is a pair
of iterators that designate the beginning and end of the computation.
A range [i,i) is an empty range; in general, a range [i,j) refers to the elements in the data structure starting with the element
pointed to by i and up to but not including the element pointed to
by j.

Emphasis mine.

Further, the description of erase you cite is not the normative text in the standard. The standard has this to say (Table 100):

a.erase(q1,q2)

Effects: Erases the elements in the range [q1, q2).

This doesn’t require that q1 be dereferenceable. If [q1, q2) is an empty range (per 24.2.1/7), then no elements are in the range, and so none are erased.