makefile/browser-asmjs: Remove now unneeded dependency to "base"
makefile/browser-asmjs: Remove now unneeded dependency to "base"

Following 09868d5 (browser-asmjs: Update to depend on existing image from
"trzeci/emscripten"), browser-asmjs does NOT depend anymore on base image.

thewtex/cross-compilers,thewtex/cross-compilers,dockcross/dockcross,dockcross/dockcross,thewtex/cross-compilers,dockcross/dockcross,thewtex/cross-compilers,dockcross/dockcross