Rochad Tlusty:
I should also add that you probably want to remove the suggestions as well, as it can create new tags based on keywords in the body (probably undesirable for you).
After taking my final exams, I found a solution for my problem.
First step: we need to look at all the files in message_boards portlet folder, then the code to create "insert tags" function is in line 308 of edit_message.jsp
<aui:input name="tags" type="assetTags" />
Our brain may raise a question: "How does this thing work? I do not understand.". For more understanding, we need to break down the tag a little into its separate parts:
_ aui
_ input
_ assetTags
Next step: These things are liferay params, so where are they? Let's look at this path:
tomcat-server\webapps\ROOT\WEB-INF\tld\liferay-ui.tld
In this file (liferay-ui.tld), we search for anything related to assetTags. After looking that file, we will see these lines
<tag>
<name>asset-tags-selector</name>
<tag-class>com.liferay.taglib.ui.AssetTagsSelectorTag</tag-class>
<body-content>JSP</body-content>
<attribute>
<name>className</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>classPK</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>contentCallback</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>curTags</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>focus</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<name>hiddenInput</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
This is what we are looking for. To find the path to the JSP, its stored in the tagclass.
<tag-class>com.liferay.taglib.ui.AssetTagsSelectorTag</tag-class>
In the java class, you'll see a variable with the path to the JSP:
private static final String _PAGE = "/html/taglib/ui/asset_tags_selector/page.jsp";
In the JSP file (page.jsp), there is a div:
<div class="lfr-tags-selector-content" id="<%= namespace + randomNamespace %>assetTagsSelector">
<aui:input name="<%= hiddenInput %>" type="hidden" />
<input class="lfr-tag-selector-input" id="<%= randomNamespace %>assetTagNames" size="15" type="text">
</div>
All we need is to add the attribute disabled="disabled" to the input tag in order to prevent any input from users.
After that, to remove "Add" button with "plus" icon, lets look at
\html\js\liferay\asset_tags_selector.js
Take a deeper look at line 398 to line 439:
var toolbar = [
/*{
handler: {
context: instance,
fn: instance._onAddEntryClick
},
icon: 'plus',
id: 'add',
label: Liferay.Language.get('add')
},*/
{
handler: {
context: instance,
fn: instance._showSelectPopup
},
icon: 'search',
id: 'select',
label: Liferay.Language.get('select')
}
];
The variable toolbar stores 3 buttons, which are add, select and suggestions, all we need is put a comment block to "add" codes like the code above.
We finish here.
it seems like a miracle 
I have been searching for it since 3 weeks ago.
