Bug 1620789 - Add source code download and build instructions to the website - remove extensions. r=me

src/dev/code-development.en.html

@@ -94,9 +94,6 @@ commands:
    git clone https://gitlab.com/seamonkey-project/seamonkey-2.53-mozilla.git mozilla-253<br>
    cd mozilla-253<br>
    git clone https://gitlab.com/seamonkey-project/seamonkey-2.53-comm.git comm<br>
-   cd extensions<br>
-   hg clone https://hg.mozilla.org/chatzilla irc<br>
-   hg clone https://hg.mozilla.org/dom-inspector inspector<br>
 </code></pre>
 
 <h3 id="future">2.57 Branch</h3>
@@ -112,8 +109,6 @@ following commands:
    hg clone https://hg.mozilla.org/releases/mozilla-esr60/ mozilla-esr60<br>
    cd mozilla-esr60<br>
    hg clone https://hg.mozilla.org/releases/comm-esr60/ comm<br>
-   cd extensions<br>
-   hg clone https://hg.mozilla.org/chatzilla irc<br>
 </code></pre>
 
 <h3 id="central">Central Branch</h3>
@@ -131,8 +126,6 @@ the following commands:
    hg clone https://hg.mozilla.org/mozilla-central/ mozilla-central<br>
    cd mozilla-central<br>
    hg clone https://hg.mozilla.org/comm-central/ comm<br>
-   cd extensions<br>
-   hg clone https://hg.mozilla.org/chatzilla irc<br>
 </code></pre>
 
 <h2 id="building">Building SeaMonkey</h2>