Remove client/input.{Buffer,Override}Stdin() functions (#4602)

Cobra's new release made them redundant.

Thanks: Juan Leni <juan.leni@zondax.ch> for the original patch.

tests/io.go

@@ -0,0 +1,21 @@
+package tests
+
+import (
+	"bytes"
+	"strings"
+
+	"github.com/spf13/cobra"
+)
+
+// ApplyMockIO replaces stdin/out/err with buffers that can be used during testing.
+func ApplyMockIO(c *cobra.Command) (*strings.Reader, *bytes.Buffer, *bytes.Buffer) {
+	mockIn := strings.NewReader("")
+	mockOut := bytes.NewBufferString("")
+	mockErr := bytes.NewBufferString("")
+	c.SetIn(mockIn)
+	c.SetOut(mockOut)
+	c.SetErr(mockErr)
+	return mockIn, mockOut, mockErr
+}
+
+// DONTCOVER