util: rename parse_usec() to parse_sec() sinds the default unit is seconds

Internally we store all time values in usec_t, however parse_usec()
actually was used mostly to parse values in seconds (unless explicit
units were specified to define a different unit). Hence, be clear about
this and name the function about what we pass into it, not what we get
out of it.

src/shared/conf-parser.c

@@ -792,7 +792,7 @@ int config_parse_path_strv(
         return 0;
 }
 
-int config_parse_usec(
+int config_parse_sec(
                 const char *filename,
                 unsigned line,
                 const char *section,
@@ -809,7 +809,7 @@ int config_parse_usec(
         assert(rvalue);
         assert(data);
 
-        if (parse_usec(rvalue, usec) < 0) {
+        if (parse_sec(rvalue, usec) < 0) {
                 log_error("[%s:%u] Failed to parse time value, ignoring: %s", filename, line, rvalue);
                 return 0;
         }