Change 'g_memmove' to 'memmove'

[stevenengler]

To remove the following warnings:

tgen/src/tgen-stream.c:424:13: warning: Deprecated pre-processor symbol, replace with
  424 |         g_memmove(buffer, stream->recv.buffer->str, amount);

http://man.hubwiz.com/docset/GLib.docset/Contents/Resources/Documents/glib-Memory-Allocation.html#g-memmove:

g_memmove has been deprecated since version 2.40 and should not be used in newly-written code.
Just use memmove().