Remove dead code in formatting.c

Remove some code guarded by IS_MINUS() or IS_PLUS(), where the entire
stanza is inside an else-block where both of these are false. This
should slightly improve test coverage.

While at it, remove coding that apparently assumes that unsetting a
bit is so expensive that we have to first check if it's already set
in the first place.

Per Coverity report from Ranier Vilela
Analysis and review by Justin Pryzby

Discussion: https://www.postgresql.org/message-id/20221223010818.GP1153%40telsasoft.com

src/backend/utils/adt/formatting.c

@@ -5664,13 +5664,9 @@ NUM_processor(FormatNode *node, NUMDesc *Num, char *inout,
 		{
 			if (Np->sign != '-')
 			{
-				if (IS_BRACKET(Np->Num) && IS_FILLMODE(Np->Num))
+				if (IS_FILLMODE(Np->Num))
 					Np->Num->flag &= ~NUM_F_BRACKET;
-				if (IS_MINUS(Np->Num))
-					Np->Num->flag &= ~NUM_F_MINUS;
 			}
-			else if (Np->sign != '+' && IS_PLUS(Np->Num))
-				Np->Num->flag &= ~NUM_F_PLUS;
 
 			if (Np->sign == '+' && IS_FILLMODE(Np->Num) && IS_LSIGN(Np->Num) == false)
 				Np->sign_wrote = true;	/* needn't sign */