Remove the negative number tests for bitwise not.

They were inadvertently relying on undefined behavior in C and we get
different results on some compilers.

Until we decide how we want the operation to behave, for now, just
leave it unspecified.

test/core/number/bitwise_not.wren

@@ -5,16 +5,10 @@ System.print(~23) // expect: 4294967272
 // Max u32 value.
 System.print(~0xffffffff) // expect: 0
 
-// Negative numbers.
-System.print(~-1) // expect: 0
-System.print(~-123) // expect: 122
-System.print(~-0xfffffffe) // expect: 4294967293
-System.print(~-0xffffffff) // expect: 4294967294
-
 // Floating point values.
 System.print(~1.23) // expect: 4294967294
 System.print(~0.00123) // expect: 4294967295
 System.print(~345.67) // expect: 4294966950
-System.print(~-12.34) // expect: 11
 
+// TODO: Negative numbers.
 // TODO: Numbers that don't fit in u32.