Revert "SILOptimizer: Replace Array.append(contentsOf: with Array.append(elem…"

[shahmishal]

Reverts #5978

We are seeing failure in following test, testing if this PR caused it.

Swift(macosx-x86_64).stdlib.Dictionary.swift
Swift(macosx-x86_64).stdlib.Set.swift

https://ci.swift.org/job/oss-swift_tools-R_stdlib-RD_test-simulator/608/

[shahmishal]

@swift-ci Please test

[shahmishal]

preset=buildbot,tools=R,stdlib=RD
@swift-ci Please test with preset

[swift-ci]

Build failed
Jenkins build - Swift Test macOS with preset
Git Commit - 5eece88
Test requested by - @shahmishal

[shahmishal]

******************** TEST 'Swift(macosx-x86_64) :: IDE/crashers/032-swift-expr-propagatelvalueaccesskind.swift' FAILED ********************
13:17:28 Script:
13:17:28 --
13:17:28 not --crash xcrun --toolchain default --sdk /Applications/Xcode-beta.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.12.sdk /Users/buildnode/jenkins/workspace/swift-PR-osx-preset/branch-master/Ninja-Release/swift-macosx-x86_64/bin/swift-ide-test -target x86_64-apple-macosx10.9  -module-cache-path '/var/folders/_8/79jmzf2142z2xydc_01btlx00000gn/T/swift-testsuite-clang-module-cachep0S2sw' -completion-cache-path '/var/folders/_8/79jmzf2142z2xydc_01btlx00000gn/T/swift-testsuite-completion-cache6DuW0G' -code-completion -code-completion-token=A -source-filename=/Users/buildnode/jenkins/workspace/swift-PR-osx-preset/branch-master/swift/validation-test/IDE/crashers/032-swift-expr-propagatelvalueaccesskind.swift
13:17:28 --