math: remove comment about aliasing lgamma as gamma

It is probably not worth supporting gamma.
(it was already deprecated in 4.3BSD)

src/math/lgamma.c

@@ -1,4 +1,4 @@
-#include "libm.h"
+#include <math.h>
 
 extern int __signgam;
 double __lgamma_r(double, int *);
@@ -7,6 +7,3 @@ double lgamma(double x)
 {
 	return __lgamma_r(x, &__signgam);
 }
-
-// FIXME
-//weak_alias(lgamma, gamma);

src/math/lgammaf.c

@@ -1,4 +1,4 @@
-#include "libm.h"
+#include <math.h>
 
 extern int __signgam;
 float __lgammaf_r(float, int *);
@@ -7,6 +7,3 @@ float lgammaf(float x)
 {
 	return __lgammaf_r(x, &__signgam);
 }
-
-// FIXME
-//weak_alias(lgammaf, gammaf);

src/math/lgammal.c

@@ -89,6 +89,8 @@
 #include "libm.h"
 
 #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
+double __lgamma_r(double x, int *sg);
+
 long double __lgammal_r(long double x, int *sg)
 {
 	return __lgamma_r(x, sg);