[class] removing redundant "constexpr-suitable" wording (#8108)

Constructors and destructors can't be coroutines (since P3533R2),
therefore they are always constexpr-suitable, and any wording
that states this explicitly is not needed and is removed in this change.

Author: hanickadot

source/classes.tex

@@ -1437,8 +1437,7 @@
 \grammarterm{compound-statement}.
 If that user-written default constructor would be ill-formed,
 the program is ill-formed.
-If that user-written default constructor would be constexpr-suitable\iref{dcl.constexpr},
-the implicitly-defined
+The implicitly-defined
 default constructor is \keyword{constexpr}.
 Before the defaulted default constructor for a class is
 implicitly defined,
@@ -1723,8 +1722,7 @@
 The copy/move constructor is implicitly defined even if the implementation elided
 its odr-use\iref{term.odr.use,class.temporary}.
 \end{note}
-If an implicitly-defined\iref{dcl.fct.def.default} constructor would be constexpr-suitable\iref{dcl.constexpr},
-the implicitly-defined
+The implicitly-defined\iref{dcl.fct.def.default}
 constructor is \keyword{constexpr}.
 
 \pnum
@@ -2220,8 +2218,7 @@
 \defnx{non-trivial}{destructor!non-trivial}.
 
 \pnum
-A defaulted destructor is a constexpr destructor
-if it is constexpr-suitable\iref{dcl.constexpr}.
+A defaulted destructor is a constexpr destructor.
 
 \pnum
 Before a