Remove z_abs(). The z_*() functions were in libf77, and for some reason

someone thought it would be a good idea to copy z_abs() to libm in 1994.
However, it's never been declared or documented anywhere, and I'm
reasonably confident that nobody uses it.

Discussed with: bde, deischen, kan

lib/msun/Symbol.map

@@ -178,7 +178,6 @@ FBSD_1.0 {
 	truncf;
 	truncl;
 	cabs;
-	z_abs;
 	cabsf;
 	drem;
 	dremf;

lib/msun/src/w_cabs.c

@@ -19,10 +19,3 @@ cabs(z)
 {
 	return hypot(creal(z), cimag(z));
 }
-
-double
-z_abs(z)
-	double complex *z;
-{
-	return hypot(creal(*z), cimag(*z));
-}