Move the SIGNASSEMBLY precompiler directive so the setting can be tak…

[BruceHaley]

…en off the command line, thus avoiding warning MSB3052.

[coveralls]

Pull Request Test Coverage Report for Build 79984

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 80.331%

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Totals
Change from base Build 79980:	0.0%
Covered Lines:	4856
Relevant Lines:	6045

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💛 - Coveralls

[fuselabs]

✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.Luis.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.AI.QnA.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.ApplicationInsights.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Azure.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.Dialogs.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Builder.TemplateManager.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Configuration.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Connector.dll compared against version 4.3.1
✔️ No Binary Compatibility issues for Microsoft.Bot.Schema.dll compared against version 4.3.1