Harmonize phrasings of "this destructor is trivial". (#2191)

Inspired by P0602 https://lichray.github.io/trivially_variant.html
Zhihao suggested that we harmonize "trivially destructible"
wording across the rest of the Standard.

Author: Quuxplusone

source/iterators.tex

@@ -2660,7 +2660,7 @@
 \effects
 The iterator is destroyed.
 If \tcode{is_trivially_destructible_v<T>} is \tcode{true},
-then this destructor is a trivial destructor.
+then this destructor is trivial.
 \end{itemdescr}
 
 \rSec3[istream.iterator.ops]{\tcode{istream_iterator} operations}

source/utilities.tex

@@ -517,9 +517,10 @@
 be a constexpr function if and only if all required element-wise
 initializations for copy and move, respectively, would satisfy the
 requirements for a constexpr function.
-The destructor of \tcode{pair} shall be a trivial destructor if
-\tcode{(is_trivially_destructible_v<T1> \&\& is_trivially_destructible_v<T2>)}
-is \tcode{true}.
+
+\pnum
+If \tcode{(is_trivially_destructible_v<T1> \&\& is_trivially_destructible_v<T2>)}
+is \tcode{true}, then the destructor of \tcode{pair} is trivial.
 
 \indexlibrary{\idxcode{pair}!constructor}%
 \begin{itemdecl}
@@ -1161,6 +1162,13 @@
 
 \rSec3[tuple.cnstr]{Construction}
 
+\pnum
+In the descriptions that follow, let $i$ be in the range
+\range{0}{sizeof...(Types)} in order, $\tcode{T}_i$
+be the $i^\text{th}$ type in \tcode{Types}, and
+$\tcode{U}_i$ be the $i^\text{th}$ type in a template parameter pack named \tcode{UTypes}, where indexing
+is zero-based.
+
 \pnum
 For each \tcode{tuple} constructor, an exception is thrown only if the construction of
 one of the types in \tcode{Types} throws an exception.
@@ -1174,16 +1182,8 @@
 constexpr functions.
 
 \pnum
-The destructor of \tcode{tuple} shall be a trivial destructor if
-\tcode{(is_trivially_destructible_v<Types> \&\& ...)}
-is \tcode{true}.
-
-\pnum
-In the constructor descriptions that follow, let $i$ be in the range
-\range{0}{sizeof...(Types)} in order, $\tcode{T}_i$
-be the $i^\text{th}$ type in \tcode{Types}, and
-$\tcode{U}_i$ be the $i^\text{th}$ type in a template parameter pack named \tcode{UTypes}, where indexing
-is zero-based.
+If \tcode{is_trivially_destructible_v<$\tcode{T}_i$>} is \tcode{true} for all $\tcode{T}_i$,
+then the destructor of \tcode{tuple} is trivial.
 
 \indexlibrary{\idxcode{tuple}!constructor}%
 \begin{itemdecl}
@@ -2544,7 +2544,7 @@
 
 \pnum
 \remarks
-If \tcode{is_trivially_destructible_v<T> == true} then this destructor shall be a trivial destructor.
+If \tcode{is_trivially_destructible_v<T>} is \tcode{true}, then this destructor is trivial.
 \end{itemdescr}
 
 \rSec3[optional.assign]{Assignment}
@@ -4162,8 +4162,8 @@
 
 \pnum
 \remarks
-If \tcode{is_trivially_destructible_v<$\tcode{T}_i$> == true} for all $\tcode{T}_i$
-then this destructor shall be a trivial destructor.
+If \tcode{is_trivially_destructible_v<$\tcode{T}_i$>} is \tcode{true} for all $\tcode{T}_i$,
+then this destructor is trivial.
 \end{itemdescr}
 
 \rSec3[variant.assign]{Assignment}