Remove Time argument from xsetsel

This is an X type and should be internal to x.c.

The selcopy() function was a single line and only used in one place, so
it was inlined to reduce LOC.

Signed-off-by: Devin J. Pohly <djpohly@gmail.com>

st.c

@@ -1747,7 +1747,7 @@ strhandle(void)
 
 				dec = base64dec(strescseq.args[2]);
 				if (dec) {
-					xsetsel(dec, CurrentTime);
+					xsetsel(dec);
 					xclipcopy();
 				} else {
 					fprintf(stderr, "erresc: invalid base64\n");