Improving labels for Sent / Received "Bytes"

The labels for Sent & Received data in the "Peers" debug panel should not be defined as "Bytes" because the units (B, KB, MB) appear after the number.  I decided to simply use "Sent" and "Received" (rather than "Data Sent" and "Data Received") because we already have translations for the former:
https://www.transifex.com/bitcoin/bitcoin/viewstrings/#ja/qt-translation-011x/47533089?q=sent
https://www.transifex.com/bitcoin/bitcoin/viewstrings/#ja/qt-translation-011x/47533089?q=received

Demo of changes:

Current UI:
    Bytes Sent      12 KB
    Bytes Received  26 MB

With this pull request:
    Sent       12 KB
    Received   26 MB

src/qt/forms/debugwindow.ui

@@ -1117,7 +1117,7 @@
           <item row="12" column="0">
            <widget class="QLabel" name="label_18">
             <property name="text">
-             <string>Bytes Sent</string>
+             <string>Sent</string>
             </property>
            </widget>
           </item>
@@ -1140,7 +1140,7 @@
           <item row="13" column="0">
            <widget class="QLabel" name="label_20">
             <property name="text">
-             <string>Bytes Received</string>
+             <string>Received</string>
             </property>
            </widget>
           </item>