link libasn1c against libmath, don't ask users to do it

libasn1c is using libm[ath] symbols from REAL.c and hence should be
linked using '-lm' to carry a dynamic linker dependency itself.

We shouldn't use a pkg-config hack to ask applications to do this on
our behalf.

Change-Id: Ie107f7252eeed90233468deaef57d3cee36abdf4
diff --git a/libasn1c.pc.in b/libasn1c.pc.in
index 89ad53a..ab0c415 100644
--- a/libasn1c.pc.in
+++ b/libasn1c.pc.in
@@ -6,6 +6,6 @@
 Name: asn1c runtime library
 Description: C Utility Library
 Version: @VERSION@
-Libs: -L${libdir} @LIBTALLOC_LIBS@ -lasn1c -lm
+Libs: -L${libdir} @LIBTALLOC_LIBS@ -lasn1c
 Cflags: -I${includedir}/ -I${includedir}/asn1c @LIBTALLOC_CFLAGS@