Update PCMDI-AMIP documentation page

[durack1]

Simplify the documentation template removing the complexity of "..different phases of CMIP7.."

[znichollscr]

Simplify the documentation template removing the complexity of "..different phases of CMIP7.."

Just noting here (in case anyone is looking) that this is pending confirmation from the core panel about whether this simplification should be done or not

[vnaik60]

Looks like we have a greenlight from John to remove the different phases of CMIP7 #222

[znichollscr]

#221 was merged but seems to have a) been lost in main somehow and b) not closed this. Just so you're aware @durack1

[durack1]

Will update this once I have the CMIP7Plus: PCMDI-AMIP-* data published - will have to cherry pick out the old goodies