Replace remaining mb*towc() calls with utf8towc().

diff --git a/toys/posix/expand.c b/toys/posix/expand.c
index a25848a..d4914ab 100644
--- a/toys/posix/expand.c
+++ b/toys/posix/expand.c

@@ -49,7 +49,7 @@
       if (CFG_TOYBOX_I18N) {
         wchar_t blah;
 
-        width = mbrtowc(&blah, toybuf+i, len-i, 0);
+        width = utf8towc(&blah, toybuf+i, len-i);
         if (width > 1) {
           if (width != fwrite(toybuf+i, width, 1, stdout))
             perror_exit("stdout");

diff --git a/toys/posix/file.c b/toys/posix/file.c
index 658708c..9958d04 100644
--- a/toys/posix/file.c
+++ b/toys/posix/file.c

@@ -267,7 +267,7 @@
     } else for (i = 0; i<len; ++i) {
       if (!(isprint(toybuf[i]) || isspace(toybuf[i]))) {
         wchar_t wc;
-        if ((bytes = mbrtowc(&wc, s+i, len-i, 0))>0 && wcwidth(wc)>=0) {
+        if ((bytes = utf8towc(&wc, s+i, len-i))>0 && wcwidth(wc)>=0) {
           i += bytes-1;
           if (!what) what = "UTF-8 text";
         } else {

diff --git a/toys/posix/paste.c b/toys/posix/paste.c
index 42e6a28..ea04f02 100644
--- a/toys/posix/paste.c
+++ b/toys/posix/paste.c

@@ -42,7 +42,6 @@
 
     // Start of each line/file resets delimiter cycle
     dpos = TT.d;
-    mbtowc(0, 0, 0);
 
     for (i = any = dcount = dlen = 0; seq || i<TT.files; i++) {
       size_t blen;
@@ -84,7 +83,7 @@
             }
           }
         } else {
-          while (0<(dlen = mbtowc(&wc, dpos, 99))) {
+          while (0<(dlen = utf8towc(&wc, dpos, 99))) {
             dpos += dlen;
             if (!(dlen = wcwidth(wc))) continue;
             if (dlen<0) dpos = dstr+1;

diff --git a/toys/posix/wc.c b/toys/posix/wc.c
index 96ff978..69c5f38 100644
--- a/toys/posix/wc.c
+++ b/toys/posix/wc.c

@@ -79,7 +79,6 @@
           wchar_t wchar;
 
           // next wide size, don't count invalid, fetch more data if necessary
-          clen = mbrtowc(&wchar, toybuf+pos, len-pos, 0);
           clen = utf8towc(&wchar, toybuf+pos, len-pos);
           if (clen == -1) continue;
           if (clen == -2 && !done) break;