Fix all duplicated keys in modules

[disenchant]

I recognised, that some modules have duplicated keys. This PR removes the first occurrence of each duplicated key as the second occurrence of it will overwrite the first one anyway. In newer versions of Ruby (e.g. 2.2.0p0) this will generate warnings:

./metasploit-framework/modules/auxiliary/scanner/http/bmc_trackit_passwd_reset.rb:134: warning: duplicated key at line 135 ignored: "SelectedQuestion"
./metasploit-framework/modules/auxiliary/scanner/http/bmc_trackit_passwd_reset.rb:136: warning: duplicated key at line 137 ignored: "answer"
./metasploit-framework/modules/auxiliary/scanner/http/bmc_trackit_passwd_reset.rb:138: warning: duplicated key at line 139 ignored: "confirmanswer"
./metasploit-framework/modules/exploits/linux/http/netgear_dgn2200b_pppoe_exec.rb:188: warning: duplicated key at line 192 ignored: "opendns_parental_ctrl"
./metasploit-framework/modules/post/windows/gather/credentials/razorsql.rb:130: warning: duplicated key at line 131 ignored: "N"

[wvu]

Thanks for getting these done. This would have been the second and final pass (#4832) for #4818.