Removed runtime ids

[akshita31]

Fixes : #1912 #1930

Changes :

1. The runtime ids for the platforms was removed in package.json, but the appropriate changes were not made in the gulpfile.js.
2. Since now same packages are being used for the Linux platforms, hence there is no need to create different objects for the various LinuxDistributions.
3. .omnisharp folder was not being cleaned as the path for the cleaning was ".omnisharp-*. Fixed it.

[rchande]

Nice work!
For comparison, can you share what the console output looks like now? (and also a final directory listing?)
How are we going to test this to make sure it doesn't get regressed again?

[akshita31]

Console Output:
[15:14:35] Starting 'clean'...
[15:14:35] Finished 'clean' after 383 ms
[15:14:35] Starting 'package:offline'...
Downloading package 'OmniSharp for Windows (.NET 4.6 / x64)' (20872 KB) .................... Done!
Downloading package '.NET Core Debugger (Windows / x64)' (39279 KB) .................... Done!
Installing package 'OmniSharp for Windows (.NET 4.6 / x64)'
Installing package '.NET Core Debugger (Windows / x64)'
Downloading package 'OmniSharp for OSX' (23790 KB) .................... Done!
Downloading package '.NET Core Debugger (macOS / x64)' (43963 KB) .................... Done!
Installing package 'OmniSharp for OSX'
Installing package '.NET Core Debugger (macOS / x64)'
Downloading package 'OmniSharp for Linux (x64)' (23673 KB) .................... Done!
Downloading package '.NET Core Debugger (linux / x64)' (55198 KB) .................... Done!
Installing package 'OmniSharp for Linux (x64)'
Installing package '.NET Core Debugger (linux / x64)'
[15:16:57] Finished 'package:offline' after 2.35 min

Final directory now contains :
csharp.1.14.0-beta2-darwin-x86_64
csharp.1.14.0-beta2-linux-x86_64
csharp.1.14.0-beta2-win32-x86_64

[rchande]

LGTM, but it would be nice if @DustinCampbell or @gregg-miskelly could sign off too.