patch 8.1.1384: using "int" for alloc() often results in compiler warnings

Problem:    Using "int" for alloc() often results in compiler warnings.
Solution:   Use "size_t" and remove type casts.  Remove alloc_check(), Vim
            only works with 32 bit ints anyway.
diff --git a/src/option.c b/src/option.c
index 39ef052..42a252e 100644
--- a/src/option.c
+++ b/src/option.c
@@ -3430,7 +3430,7 @@
 	cdpath = vim_getenv((char_u *)"CDPATH", &mustfree);
 	if (cdpath != NULL)
 	{
-	    buf = alloc((unsigned)((STRLEN(cdpath) << 1) + 2));
+	    buf = alloc((STRLEN(cdpath) << 1) + 2);
 	    if (buf != NULL)
 	    {
 		buf[0] = ',';	    /* start with ",", current dir first */
@@ -7913,7 +7913,7 @@
 	wp->w_p_cc_cols = NULL;
     else
     {
-	wp->w_p_cc_cols = (int *)alloc((unsigned)sizeof(int) * (count + 1));
+	wp->w_p_cc_cols = (int *)alloc(sizeof(int) * (count + 1));
 	if (wp->w_p_cc_cols != NULL)
 	{
 	    /* sort the columns for faster usage on screen redraw inside
@@ -10053,8 +10053,8 @@
 #define INC 20
 #define GAP 3
 
-    items = (struct vimoption **)alloc((unsigned)(sizeof(struct vimoption *) *
-								PARAM_COUNT));
+    items = (struct vimoption **)alloc(sizeof(struct vimoption *)
+								* PARAM_COUNT);
     if (items == NULL)
 	return;
 
@@ -11941,7 +11941,7 @@
 		*num_file = num_term;
 	    else
 		return OK;
-	    *file = (char_u **)alloc((unsigned)(*num_file * sizeof(char_u *)));
+	    *file = (char_u **)alloc(*num_file * sizeof(char_u *));
 	    if (*file == NULL)
 	    {
 		*file = (char_u **)"";
@@ -11959,7 +11959,7 @@
     char_u  *buf;
 
     *num_file = 0;
-    *file = (char_u **)alloc((unsigned)sizeof(char_u *));
+    *file = (char_u **)alloc(sizeof(char_u *));
     if (*file == NULL)
 	return FAIL;
 
@@ -12822,7 +12822,7 @@
 	return FALSE;
     }
 
-    *array = (int *)alloc((unsigned) ((valcount + 1) * sizeof(int)));
+    *array = (int *)alloc((valcount + 1) * sizeof(int));
     if (*array == NULL)
 	return FALSE;
     (*array)[0] = valcount;
@@ -13045,7 +13045,7 @@
 
     if (oldts == NULL)
 	return NULL;
-    newts = (int *)alloc((unsigned)((oldts[0] + 1) * sizeof(int)));
+    newts = (int *)alloc((oldts[0] + 1) * sizeof(int));
     if (newts != NULL)
 	for (t = 0; t <= oldts[0]; ++t)
 	    newts[t] = oldts[t];