Fix unintentional duplicate code block prefixes (#36)

* Fix unintentional duplicate code block prefix in first_steps.md

* Similar fix in first_steps/challenges.md

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Co-authored-by: Ethan McCue <[email protected]>

Author: slovdahl

src/first_steps.md

@@ -16,7 +16,6 @@ Its a tradition for this to be your first program in any language.
 We aren't quite at the point where I can explain what `void main()` means, but
 all you need to know for now is that it is what Java looks for to know where to start the program.
 
-```java,no_run
 ```java,no_run
 void main() {
     < WRITE YOUR CODE HERE >

src/first_steps/challenges.md

@@ -12,7 +12,6 @@ The rules for this are
 
 Write a program that prints your name twice. So if your name is "Jasmine", the output of the program should be this.
 
-```text,no_run
 ```text,no_run
 Jasmine
 Jasmine