MDEV-18115: Remove some redundant comparisons

Now that FIL_TYPE_LOG no longer exists, let us remove some redundant
comparisons of fil_space_t::purpose.

fil_flush_low(): Do not distinguish FIL_TYPE_TEMPORARY.

fil_space_get_space(): Assume that space->purpose is valid.

storage/innobase/fil/fil0fil.cc

@@ -711,15 +711,8 @@ static void fil_flush_low(fil_space_t* space, bool metadata = false)
 
 		ut_a(node->is_open());
 
-		switch (space->purpose) {
-		case FIL_TYPE_TEMPORARY:
-			ut_ad(0); // we already checked for this
-			/* fall through */
-		case FIL_TYPE_TABLESPACE:
-		case FIL_TYPE_IMPORT:
-			fil_n_pending_tablespace_flushes++;
-			break;
-		}
+		fil_n_pending_tablespace_flushes++;
+
 #ifdef _WIN32
 		if (node->is_raw_disk) {
 
@@ -749,16 +742,7 @@ static void fil_flush_low(fil_space_t* space, bool metadata = false)
 			}
 		}
 
-		switch (space->purpose) {
-		case FIL_TYPE_TEMPORARY:
-			break;
-		case FIL_TYPE_TABLESPACE:
-		case FIL_TYPE_IMPORT:
-			fil_n_pending_tablespace_flushes--;
-			continue;
-		}
-
-		ut_ad(0);
+		fil_n_pending_tablespace_flushes--;
 	}
 
 	space->n_pending_flushes--;
@@ -1387,13 +1371,7 @@ fil_space_get_space(
 		return(space);
 	}
 
-	switch (space->purpose) {
-	case FIL_TYPE_TEMPORARY:
-	case FIL_TYPE_TABLESPACE:
-	case FIL_TYPE_IMPORT:
-		space = fil_system.read_page0(id);
-	}
-
+	space = fil_system.read_page0(id);
 	return(space);
 }