sagemathgh-39186: Remove backslash hack in doctest
    
Would fix sagemath#39058 . I think it's
cleaner to remove this thing anyway (given that it doesn't work in the
real Sage command prompt either)

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URL: sagemath#39186
Reported by: user202729
Reviewer(s): Tobias Diez

Author: Release Manager

src/doc/en/developer/coding_basics.rst

@@ -1114,12 +1114,10 @@ written.
     The :ref:`doctest fixer <section-fixdoctests-optional-needs>` uses
     tab stops at columns 48, 56, 64, ... for these tags.
 
-- **Split long lines:** You may want to split long lines of code with a
-  backslash. Note: this syntax is non-standard and may be removed in the
-  future::
+- **Split long lines:** Standard Python rules apply. For example::
 
-      sage: n = 123456789123456789123456789\
-      ....:     123456789123456789123456789
+      sage: n = (123456789123456789123456789 +
+      ....:      123456789123456789123456789)
       sage: n.is_prime()
       False
 

src/doc/en/thematic_tutorials/lie/branching_rules.rst

@@ -344,7 +344,7 @@ we could accomplish the branching in two steps, thus::
     sage: A1xA1 = WeylCharacterRing("A1xA1", style="coroots")
     sage: reps = [A3(fw) for fw in A3.fundamental_weights()]
     sage: [pi.branch(C2, rule="symmetric").branch(B2, rule="isomorphic"). \
-             branch(D2, rule="extended").branch(A1xA1, rule="isomorphic") for pi in reps]
+    ....:    branch(D2, rule="extended").branch(A1xA1, rule="isomorphic") for pi in reps]
     [A1xA1(1,0) + A1xA1(0,1), 2*A1xA1(0,0) + A1xA1(1,1), A1xA1(1,0) + A1xA1(0,1)]
 
 As you can see, we've redone the branching rather circuitously this