[simd.overview] Remove obsolete "noexcept" (#8250)

The "noexcept" specifier was removed from the design by P3430R0,
but the paper omitted the corresponding change of the synopsis.

Author: hewillk

source/numerics.tex

@@ -17588,7 +17588,7 @@
     template<class U, class UAbi>
       constexpr explicit(@\seebelow@) basic_vec(const basic_vec<U, UAbi>&) noexcept;
     template<class G>
-      constexpr explicit basic_vec(G&& gen) noexcept;
+      constexpr explicit basic_vec(G&& gen);
     template<class R, class... Flags>
       constexpr basic_vec(R&& range, flags<Flags...> = {});
     template<class R, class... Flags>
@@ -20052,7 +20052,7 @@
     template<size_t UBytes, class UAbi>
       constexpr explicit basic_mask(const basic_mask<UBytes, UAbi>&) noexcept;
     template<class G>
-      constexpr explicit basic_mask(G&& gen) noexcept;
+      constexpr explicit basic_mask(G&& gen);
     constexpr basic_mask(const bitset<size()>& b) noexcept;
     constexpr explicit basic_mask(@\libconcept{unsigned_integral}@ auto val) noexcept;