xdiff-interface.c: always trim trailing space from xfuncname matches

xdiff-interface.c: always trim trailing space from xfuncname matches

Generally, trailing space is removed from the string matched by the
xfuncname patterns.  The exception is when the matched string exceeds the
length of the fixed-size buffer that it will be copied in to.  But, a
string that exceeds the buffer can still contain trailing space in the
portion of the string that will be copied into the buffer.  So, simplify
this code slightly, and just perform the trailing space removal always.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>