libstdc++: Remove __gnu_cxx::rope::erase(size_type) [PR102048]

libstdc++: Remove __gnu_cxx::rope::erase(size_type) [PR102048]

This function claims to remove a single character at index p, but it
actually removes p+1 characters beginning at p. So r.erase(0) removes
the first character, but r.erase(1) removes the second and third, and
r.erase(2) removes the second, third and fourth. This is not a useful
API.

The overload is present in the SGI STL <stl_rope.h> header that we
imported, but it isn't documented in the API reference. The erase
overloads that are documented are:

erase(const iterator& p)
erase(const iterator& f, const iterator& l)
erase(size_type i, size_type n);

Having an erase(size_type p) overload that erases a single character (as
the comment says it does) might be useful, but would be inconsistent
with std::basic_string::erase(size_type p = 0, size_type n = npos),
which erases from p to the end of the string when called with a single
argument.

Since the function isn't part of the documented API, doesn't do what it
claims to do (or anything useful) and "fixing" it would leave it
inconsistent with basic_string, I'm just removing that overload.

libstdc++-v3/ChangeLog:

	PR libstdc++/102048
	* include/ext/rope (rope::erase(size_type)): Remove broken
	function.