Remove GCC version pinning. (#2316)

Summary:
Pull Request resolved: #2316

## Context
The current build pipeline is broken because the coordinator image can't find that version of GCC. GCC is needed for the pip installs of the thrift libraries.

Reviewed By: ztlbells

Differential Revision: D47021168

fbshipit-source-id: 9091549cbd87d28f27ed4cb951e69754b24d9f94

fbpcs/Dockerfile

@@ -10,7 +10,7 @@ RUN apt-get update
 RUN apt-get install -y software-properties-common
 RUN apt-get update && apt-get install -y \
     awscli \
-    gcc=4:10.2.1-1 \
+    gcc \
     git \
     unzip \
     vim