[time.clock.system] Remove periods from impldef index entries.

Author: Eelis

source/utilities.tex

@@ -12468,7 +12468,7 @@
 \tcode{time_point}.
 It is implementation defined whether values are rounded or truncated to the
 required precision.\indeximpldef{whether values are rounded or truncated to the
-required precision when converting between \tcode{time_t} values and \tcode{time_point} objects.}
+required precision when converting between \tcode{time_t} values and \tcode{time_point} objects}
 \end{itemdescr}
 
 \indexlibrary{\idxcode{from_time_t}}%
@@ -12483,7 +12483,7 @@
 \tcode{time_point}.
 It is implementation defined whether values are rounded or truncated to the
 required precision.\indeximpldef{whether values are rounded or truncated to the
-required precision when converting between \tcode{time_t} values and \tcode{time_point} objects.}
+required precision when converting between \tcode{time_t} values and \tcode{time_point} objects}
 \end{itemdescr}
 
 \rSec3[time.clock.steady]{Class \tcode{steady_clock}}