basic: move shared/sysctl-util.[ch] → basic/

This is self-contained ans allows us later to use the provided APIs from
other code in src/basic/

src/basic/meson.build

@@ -237,6 +237,8 @@ basic_sources = files('''
         strv.h
         strxcpyx.c
         strxcpyx.h
+        sysctl-util.c
+        sysctl-util.h
         syslog-util.c
         syslog-util.h
         terminal-util.c

src/shared/meson.build

@@ -242,8 +242,6 @@ shared_sources = files('''
         specifier.h
         switch-root.c
         switch-root.h
-        sysctl-util.c
-        sysctl-util.h
         tmpfile-util-label.c
         tmpfile-util-label.h
         tomoyo-util.c