Remove unused Projection operator (#1543)

Author: GromNaN

.gitattributes

@@ -22,6 +22,5 @@ rector.php export-ignore
 /src/Builder/Accumulator/*.php linguist-generated=true
 /src/Builder/Expression/*.php linguist-generated=true
 /src/Builder/Query/*.php linguist-generated=true
-/src/Builder/Projection/*.php linguist-generated=true
 /src/Builder/Stage/*.php linguist-generated=true
 /tests/Builder/*/Pipelines.php linguist-generated=true

psalm-baseline.xml

@@ -90,11 +90,6 @@
       <code><![CDATA[$value]]></code>
     </MixedAssignment>
   </file>
-  <file src="src/Builder/Projection/ElemMatchOperator.php">
-    <MixedArgumentTypeCoercion>
-      <code><![CDATA[$query]]></code>
-    </MixedArgumentTypeCoercion>
-  </file>
   <file src="src/Builder/Query.php">
     <ArgumentTypeCoercion>
       <code><![CDATA[$query]]></code>