Revert "ExprBytesOps: also test the bytes.to_s(encoding) method"

This reverts commit 1d8116f.

I'm reverting this for "compatibility reasons": it turned out that the
U+00A0 character was causing chaos in a number of target languages and
our CI infrastructure, which wasn't really the point. I've described the
cause in kaitai-io/kaitai_struct#1133. I will
probably cover this case in a separate test sometime in the future.

formats/expr_bytes_ops.ksy

@@ -19,8 +19,6 @@ instances:
     value: one.min
   one_max:
     value: one.max
-  one_to_s:
-    value: one.to_s('IBM866')
 
   two_size:
     value: two.size
@@ -34,5 +32,3 @@ instances:
     value: two.min
   two_max:
     value: two.max
-  two_to_s:
-    value: two.to_s('IBM866')

spec/ks/expr_bytes_ops.kst

@@ -19,8 +19,6 @@ asserts:
     expected: 0xff
   - actual: one_max.to_s
     expected: '"255"'
-  - actual: one_to_s
-    expected: '"\u0001\u0042\u00a0"'
 
   # two = [0x41, 0xff, 0x4b]
 
@@ -40,5 +38,3 @@ asserts:
     expected: 0xff
   - actual: two_max.to_s
     expected: '"255"'
-  - actual: two_to_s
-    expected: '"\u0041\u00a0\u004b"'