man: Remove duplicate word in dpkg-buildflags(1)

Signed-off-by: Guillem Jover <guillem@debian.org>

man/dpkg-buildflags.pod

@@ -183,7 +183,7 @@ the flag is set/modified by an environment-specific configuration.
 Print any information that can be useful to explain the behaviour of the
 program: current vendor, relevant environment variables, feature areas,
 state of all feature flags, whether a feature is handled as a builtin
-default by the compiler (since dpkg dpkg 1.21.14),
+default by the compiler (since dpkg 1.21.14),
 and the compiler flags with their origin (since dpkg 1.19.0).
 
 For example: