Revert "Introduce and use SWIFT_HAVE_LIBEDIT"

[shahmishal]

Reverts #6459

We are seeing failure on master, it might be related to this PR. Testing if reverting this PR fixes the issue.

[shahmishal]

@swift-ci Please test

[shahmishal]

@swift-ci Please test

[swift-ci]

Build failed
Jenkins build - Swift Test OS X Platform
Git Commit - ef49338
Test requested by - @shahmishal

[swift-ci]

Build failed
Jenkins build - Swift Test Linux Platform
Git Commit - ef49338
Test requested by - @shahmishal

[swift-ci]

Build failed
Jenkins build - Swift Test OS X Platform
Git Commit - ef49338
Test requested by - @shahmishal

[shahmishal]

@mxswd @hughbe We are reverting these commits because its causing following test failures:
ef49338
f7b1cbc

13:08:55 Failing Tests (10):
13:08:55     Swift(macosx-x86_64) :: DebugInfo/variables-repl.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_13695499.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_17597453.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_autolinking.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_conformance_lookup.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_diagnostics.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/repl_hashbang.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/SDK/Cocoa_repl.swift
13:08:55     Swift(macosx-x86_64) :: Interpreter/SDK/missing_imports_repl.swift