move src/shared/rlimit-util.[ch] → src/basic/

This is really basic stuff and in a follow-up commit will use it all
across the codebase, including in process-util.[ch] which is in
src/basic/. Hence let's move it back to src/basic/ itself.

src/basic/meson.build

@@ -120,6 +120,8 @@ basic_sources = files('''
         refcnt.h
         replace-var.c
         replace-var.h
+        rlimit-util.c
+        rlimit-util.h
         rm-rf.c
         rm-rf.h
         securebits.h

src/shared/meson.build

@@ -118,8 +118,6 @@ shared_sources = files('''
         reboot-util.h
         resolve-util.c
         resolve-util.h
-        rlimit-util.c
-        rlimit-util.h
         seccomp-util.h
         securebits-util.c
         securebits-util.h