rm "I/O error" error msg; just keep >0 exit status (re: 9011fa93)

The bug was really that I/O errors in output builtins were
undetectable by any means. Having a >0 exit status is sufficient.
Adding an error message risks making existing ksh scripts noisier,
or even breaking them if they redirect stderr to stdout.

Note to self: in future, implement the minimum change necessary to
fix bugs, nothing more. The fact that I needed to add four extra
2>/dev/null to the regression tests should have been a hint.

src/cmd/ksh93/bltins/print.c,
src/cmd/ksh93/data/msg.c,
src/cmd/ksh93/include/io.h:
- Remove "I/O error" message.

src/cmd/ksh93/tests/builtins.sh:
- Update to check for exit status only.

src/cmd/ksh93/tests/basic.sh,
src/cmd/ksh93/tests/coprocess.sh:
- Revert four new '2>/dev/null' to suppress the error message.

(cherry picked from commit 5e17be24d18455b575b6e98bc631c6935ffc795a)

src/cmd/ksh93/tests/basic.sh

@@ -446,7 +446,7 @@ done | while read sec; do ( "$binsleep" "$sec"; "$binsleep" "$sec") done
 s=SECONDS
 set -o pipefail
 for ((i=0; i < 30; i++))
-do	print hello 2>/dev/null
+do	print hello
 	sleep .01
 done |  "$binsleep" .1
 (( (SECONDS-s) < .2 )) || err_exit 'early termination not causing broken pipe'
@@ -486,7 +486,7 @@ bintrue=$(whence -p true)
 set -o pipefail
 float start=$SECONDS end 
 for ((i=0; i < 2; i++))
-do	print foo 2>/dev/null
+do	print foo
 	sleep .15
 done | { read; $bintrue; end=$SECONDS ;}
 (( (SECONDS-start) < .1 )) && err_exit "pipefail not waiting for pipe to finish"

src/cmd/ksh93/tests/builtins.sh

@@ -662,8 +662,8 @@ actual=$(
         ) | true
     } 2>&1
 )
-expect=$': print: I/O error\n1'
-if [[ $actual != *"$expect" ]]
+expect='1'
+if [[ $actual != "$expect" ]]
 then
     err_exit "I/O error not detected: expected $(printf %q "$expect"), got $(printf %q "$actual"))"
 fi

src/cmd/ksh93/tests/coprocess.sh

@@ -272,7 +272,7 @@ _COSHELL_msgfd=5
 function cop
 {
 	read
-	print ok 2>/dev/null
+	print ok
 }
 
 exp=ok
@@ -348,7 +348,7 @@ wait
 function cop
 {
         read
-        print ok 2>/dev/null
+        print ok
 }
 exp=ok
 cop |&