shared/conf-parser: collapse pkgdir and conf_file args into one

This essentially reverts 5656cdfeea. I find it
much easier to understand what is going on when the
path-relative-to-the-search-path is passed in full, instead of being constructed
from two parts, with one of the parts being implicit in some places.

Also, we call 'systemd-analyze cat-config <path>' with <path> with the same
meaning, so this makes the internal and external APIs more consistent.

src/shared/conf-parser.c

@@ -600,9 +600,8 @@ static int config_parse_many_files(
 
 /* Parse one main config file located in /etc/$pkgdir and its drop-ins, which is what all systemd daemons
  * do. */
-int config_parse_config_file_full(
+int config_parse_config_file(
                 const char *conf_file,
-                const char *pkgdir,
                 const char *sections,
                 ConfigItemLookup lookup,
                 const void *table,
@@ -614,7 +613,6 @@ int config_parse_config_file_full(
         int r;
 
         assert(conf_file);
-        assert(pkgdir);
 
         /* build the dropin dir list */
         dropin_dirs = new0(char*, strv_length(conf_paths) + 1);
@@ -628,10 +626,10 @@ int config_parse_config_file_full(
         STRV_FOREACH(p, conf_paths) {
                 char *d;
 
-                d = strjoin(*p, pkgdir, "/", conf_file, ".d");
+                d = strjoin(*p, conf_file, ".d");
                 if (!d) {
                         if (flags & CONFIG_PARSE_WARN)
-                                return log_oom();
+                                log_oom();
                         return -ENOMEM;
                 }
 
@@ -642,7 +640,7 @@ int config_parse_config_file_full(
         if (r < 0)
                 return r;
 
-        const char *sysconf_file = strjoina(SYSCONF_DIR, "/", pkgdir, "/", conf_file);
+        const char *sysconf_file = strjoina(SYSCONF_DIR, "/", conf_file);
 
         return config_parse_many_files(STRV_MAKE_CONST(sysconf_file), dropins,
                                        sections, lookup, table, flags, userdata, NULL);