utils/pmx/pmx-2.6.18/libf2c/f2c.h: remove unnecesary macro for abs()

On POSIX systems, abs() is a function provided by your C Standard library,
so we don't need to define it as a macro.  It is dangerous to do so because
if f2c.h is included before stdlib.h, then then macro breaks the function
prototype.

We just remove it.

Signed-off-by: Anthony G. Basile <blueness@gentoo.org>

diff -Naur texlive-20120701-source.orig/utils/pmx/pmx-2.6.18/libf2c/f2c.h texlive-20120701-source/utils/pmx/pmx-2.6.18/libf2c/f2c.h
--- texlive-20120701-source.orig/utils/pmx/pmx-2.6.18/libf2c/f2c.h	2012-05-20 10:47:27.000000000 +0000
+++ texlive-20120701-source/utils/pmx/pmx-2.6.18/libf2c/f2c.h	2014-05-15 17:16:37.030402773 +0000
@@ -157,7 +157,6 @@
 	};
 typedef struct Namelist Namelist;
 
-#define abs(x) ((x) >= 0 ? (x) : -(x))
 #define dabs(x) (doublereal)abs(x)
 #define min(a,b) ((a) <= (b) ? (a) : (b))
 #define max(a,b) ((a) >= (b) ? (a) : (b))