Replace go 1.7.3 compiler with go 1.7.4 compiler

Also remove old 1.4.2 and 1.5.1 compilers which aren't used anymore.
(We still keep the bootstrap 1.4.2 compiler of course).

Change-Id: I7f8ea2a435466d903637e1fc29d64511145a5232
diff --git a/host-golang-2f6557233c5a5c311547144c34b4045640ff9f71.tar.gz b/host-golang-2f6557233c5a5c311547144c34b4045640ff9f71.tar.gz
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--- a/host-golang-2f6557233c5a5c311547144c34b4045640ff9f71.tar.gz
+++ /dev/null
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diff --git a/host-golang-6b36535cf382bce845dd2d272276e7ba350b0c6b.tar.gz b/host-golang-6b36535cf382bce845dd2d272276e7ba350b0c6b.tar.gz
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diff --git a/host-golang-883bc6ed0ea815293fe6309d66f967ea60630e87.tar.gz b/host-golang-883bc6ed0ea815293fe6309d66f967ea60630e87.tar.gz
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index fa15dcf..0000000
--- a/host-golang-883bc6ed0ea815293fe6309d66f967ea60630e87.tar.gz
+++ /dev/null
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diff --git a/host-golang-f2e4c8b5fb3660d793b2c545ef207153db0a34b1.tar.gz b/host-golang-f2e4c8b5fb3660d793b2c545ef207153db0a34b1.tar.gz
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+++ /dev/null
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