Removed .mt file extension and example since there are more languages that use this.

lib/linguist/languages.yml

@@ -1761,7 +1761,6 @@ Mathematica:
   - .cdf
   - .m
   - .ma
-  - .mt
   - .nb
   - .nbp
   - .wl

samples/Mathematica/UnitTest.mt

@@ -1,17 +0,0 @@
-BeginTestSection["Untitled-5"]
-
-VerificationTest[(* 1 *)
-	RotationMatrix[phi]
-	,
-	List[List[Cos[phi], Times[-1, Sin[phi]]], List[Sin[phi], Cos[phi]]]	
-]
-
-VerificationTest[(* 2 *)
-	Times[1, Power[Plus[a, Times[-1, a]], -1]]
-	,
-	ComplexInfinity
-	,
-	{Power::infy}
-]
-
-EndTestSection[]