Partially revert ac76bc1145 because it is no longer necessary

In ac76bc1145, I added a few volatiles to work around ctrig_test
failures with {inf,inf}. This is not necessary anymore now, since in
3b00222f15 we added -fp-exception-behavior=maytrap for clang >= 10 in
libm's Makefile. (The flag tells clang to use stricter floating point
semantics, which libm depends on.)

PR:		244732, 254911
Fixes:		ac76bc1145
MFC after:	3 days

lib/msun/src/s_ccoshf.c

@@ -43,7 +43,7 @@ static const float huge = 0x1p127;
 float complex
 ccoshf(float complex z)
 {
-	volatile float x, y, h;
+	float x, y, h;
 	int32_t hx, hy, ix, iy;
 
 	x = crealf(z);

lib/msun/src/s_ctanh.c

@@ -76,7 +76,7 @@ __FBSDID("$FreeBSD$");
 double complex
 ctanh(double complex z)
 {
-	volatile double x, y;
+	double x, y;
 	double t, beta, s, rho, denom;
 	uint32_t hx, ix, lx;
 

lib/msun/src/s_ctanhf.c

@@ -41,7 +41,7 @@ __FBSDID("$FreeBSD$");
 float complex
 ctanhf(float complex z)
 {
-	volatile float x, y;
+	float x, y;
 	float t, beta, s, rho, denom;
 	uint32_t hx, ix;