GHA: remove DEVTOOLS_ROOT property

Remove the use of the `DEVTOOLS_ROOT` property when building the
installer MSIs. References to this have been removed from the WiX
projects as of swiftlang/swift-installer-scripts#347.

Author: compnerd

.github/workflows/swift-toolchain.yml

@@ -3300,7 +3300,6 @@ jobs:
               -p:SignOutput=${{ inputs.signed }} `
               -p:CERTIFICATE=${env:CERTIFICATE} `
               -p:PASSPHRASE=${{ secrets.PASSPHRASE }} `
-              -p:DEVTOOLS_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:TOOLCHAIN_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:ENABLE_MIMALLOC=${{ matrix.arch == 'amd64' && 'true' || 'false' }} `
               -p:ProductArchitecture=${{ matrix.arch }} `
@@ -3315,7 +3314,6 @@ jobs:
               -p:SignOutput=${{ inputs.signed }} `
               -p:CERTIFICATE=${env:CERTIFICATE} `
               -p:PASSPHRASE=${{ secrets.PASSPHRASE }} `
-              -p:DEVTOOLS_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:TOOLCHAIN_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:ProductArchitecture=${{ matrix.arch }} `
               -p:ProductVersion=${{ inputs.swift_version }} `
@@ -3329,7 +3327,6 @@ jobs:
               -p:SignOutput=${{ inputs.signed }} `
               -p:CERTIFICATE=${env:CERTIFICATE} `
               -p:PASSPHRASE=${{ secrets.PASSPHRASE }} `
-              -p:DEVTOOLS_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:TOOLCHAIN_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:INCLUDE_SWIFT_INSPECT=true `
               -p:SWIFT_INSPECT_BUILD=${{ github.workspace }}/BuildRoot/DebuggingTools/swift-inspect `
@@ -3345,7 +3342,6 @@ jobs:
               -p:SignOutput=${{ inputs.signed }} `
               -p:CERTIFICATE=${env:CERTIFICATE} `
               -p:PASSPHRASE=${{ secrets.PASSPHRASE }} `
-              -p:DEVTOOLS_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:TOOLCHAIN_ROOT=${{ github.workspace }}/BuildRoot/Library/Developer/Toolchains/unknown-Asserts-development.xctoolchain `
               -p:ProductArchitecture=${{ matrix.arch }} `
               -p:ProductVersion=${{ inputs.swift_version }} `